What does the research say?
In cell and animal studies, cannabis compounds showed intriguing effects on cancer cells; however, these findings have not been borne out in human studies.
The most reliable data in humans come from a study comparing pure CBD oil with an inactive drug (placebo) in patients with advanced cancer. When this study's data were analyzed separately, no difference was seen between the two groups in disease progression or survival. Positive results were reported in a case series of 15 patients with a brain tumor (glioblastoma) and in another series of 119 patients with various cancers; however, there was no comparison group, and most patients were receiving standard cancer treatment at the same time. The American Society of Clinical Oncology (ASCO) points out that in the 119-patient series, those treated for less than 6 months were excluded and concurrent treatment was disregarded. In a review of 77 published case reports, 81% of the cases were judged weak for showing an effect of cannabis; only 14% (11 cases) reported that the cancer was active when cannabis was started, that the response was confirmed by lab tests or imaging, and that no other cancer treatment was received in the same period.
In a small safety study with a purified CBD medicine in 21 patients whose PSA rose again after prostate cancer treatment, at 3 months PSA stayed stable in most patients (rose by less than 25%, by the study's definition) and fell in one; imaging showed disease progression in 3 patients, in two of them after the study ended. Because there was no comparison group, this does not mean that CBD stopped the cancer; the study was done mainly to measure whether the medicine is safe.
A small study in which a mouth spray containing THC and CBD was tried together with chemotherapy in glioblastoma was done mainly to measure safety and is not suitable for drawing conclusions about survival. To answer this question, enrollment was completed in October 2026 in a larger study of 122 patients; as of October 2026, its results have not been published. In 2024, the American Society of Clinical Oncology (ASCO) states as a strong recommendation that cannabis products should not be used in place of cancer treatment; it also does not recommend them for supporting treatment outside of clinical trials.
Other small studies with THC-containing products also failed to show an effect on tumors. Two different THC:CBD ratios were compared in 88 patients with high-grade glioma; at week 12, the tumor shrank in about one in ten patients, but there was no comparison group not taking cannabis, and no difference was seen between the two ratios. In chronic lymphocytic leukemia, a single dose of THC and CBD spray slightly reduced cancer cells in the blood for only a few hours; the researchers saw no therapeutic potential. The first study, in which THC was delivered into the tumor in 9 patients with glioblastoma, also had no comparison group.
The results of observational studies comparing cancer patients who use and do not use cannabis are inconsistent. In three of six studies in patients receiving immune therapy (immunotherapy), response or survival was worse in those using cannabis; in three, there was no difference or only a slight advantage on one measure. An independent analysis that re-examined two Israeli studies with negative results reported that most of the p-values in the baseline tables could not be obtained with the test stated in the article, and found group differences not reported in the articles: cannabis users were younger, more often received immunotherapy as a second or later line, and numerically more of them smoked. Because raw data were not available, the main results could not be recalculated. In people taking a targeted drug (PARP inhibitor) for ovarian cancer, no link was found between cannabis use and the course of the disease. In studies reporting better outcomes in people taking THC in palliative care, in cannabis oil users in Thailand and in cannabis oil users with prostate cancer in South Africa, the groups were formed not at random but according to patients' condition or preference; the authors themselves note that these differences could explain the result. Studies of this kind do not show cause and effect.
Course of cancer in people who use cannabis: The studies in the previous paragraph looked at the use of cannabis during cancer treatment. There are also a few observational studies that looked at whether the disease takes a different course in people who were already using cannabis when they were diagnosed with cancer (some of them together with tobacco). In Canada, 47 patients with HPV-related cancer of the middle part of the throat (oropharynx) who used cannabis regularly were compared with 47 patients of similar age, sex and disease stage; over about 4 years of follow-up, there was no difference in survival or in the disease coming back. In another study from the same center with 513 head and neck cancer patients, a second head and neck cancer was not more common in cannabis users (in 2 of 59 people; the number of events is very small). In a study in France of about 9,000 people diagnosed with lung cancer, those who smoked cannabis were diagnosed on average about 15 years younger than those who smoked only tobacco; when people of similar age, stage and amount of smoking were compared, survival was not different. Also in France, among 148 lung cancer patients aged 60 or younger, all of those who smoked cannabis also smoked tobacco; compared with people who smoked only tobacco in similar amounts, rare and aggressive tumor types (17% versus 4%) and emphysema in the lungs were more common in them; this study looked at features at the time of diagnosis, not at survival. In the US, among 1,472 patients with bladder cancer, no link was seen between cannabis use and the cancer coming back in the first 2 years (in the same study, smoking for a long time increased the risk). These studies do not show that cannabis cures or worsens cancer: the groups were not formed by lottery, cannabis use relies mostly on people's own reports, how much and which product was used is not known, and the share of tobacco, alcohol or factors such as HPV cannot be fully separated. That is why the strength of the evidence on this question is very weak.
Strength of evidence: ○○○○ Insufficient evidence. Finding: No effect found. What does this mean?
Ongoing research on this topic
Trials testing CBD for this topic on ClinicalTrials.gov: 11 under way (7 recruiting); results are awaited from 2 that ended in the last two years. A trial being under way does not show that CBD works.
- NCT07459920: Phase 2, not yet recruiting, target 156 participants
- NCT06731894: Phase 2, recruiting, target 120 participants
- NCT05754840: Phase 1/2, recruiting, target 60 participants
Registries in other countries also list 1 recruiting trial on this topic: other registries.
Possible side effects and drug interactions
The most important risk of using CBD during cancer treatment is drug interactions. CBD can slow down how some medicines are broken down in the body: everolimus levels were shown to rise about 2.5-fold; levels of tacrolimus and sirolimus can also rise. In a patient using CBD and taking tamoxifen, the active form of tamoxifen in the body was reported to be low.
In some observational studies in patients receiving immune therapy (immunotherapy), those using cannabis, mostly THC-containing, had a lower response rate to treatment (15.9% vs. 37.5% in one study) or shorter survival; other studies found no difference. It has not been proven that this was caused by cannabis, and there are no data specific to pure CBD. With a spray containing THC and CBD, vomiting, dizziness, tiredness, nausea and headache were reported.
Interactions with medicines used for this condition
Interactions reported for these medicines in peer-reviewed publications and official prescribing information. A medicine that is not listed can still interact with CBD; tell your doctor about every medicine you take.
| Medicine | Importance | Warning | Source |
|---|---|---|---|
| Everolimus | High importance | Everolimus, sirolimus: In a controlled study in healthy volunteers taking approved CBD, the blood level of everolimus rose about 2.5-fold; in patients with TSC (tuberous sclerosis complex), everolimus and sirolimus levels rose in most patients when CBD was added. The prescribing information for both medicines recommends close monitoring of blood levels with CBD, and lowering the dose if needed. Do not start without talking to your doctor; your drug level should be monitored. | EMA Epidyolex SmPC 4.5, PMID 37132402, PMID 31924480, Everolimus (Afinitor) prescribing information §2.11 and §7.1, dailymed.nlm.nih.gov, Everolimus (Zortress) prescribing information §5.22 and §7.1, dailymed.nlm.nih.gov, Sirolimus prescribing information §5.21 and §7.5, dailymed.nlm.nih.gov |
| Warfarin | High importance | Warfarin: If you take warfarin, tell your doctor before starting CBD. Case reports have described INR rising and the warfarin dose needing to be lowered; more frequent INR monitoring is recommended. | PMID 29387536, PMID 33016308, PMID 30326170 |
| Immunotherapy (checkpoint inhibitors, e.g., nivolumab) | Caution | Immunotherapy (checkpoint inhibitors): In some observational studies, cannabis users had a lower response to immunotherapy or shorter survival; other studies found no difference, and the results conflict. Cause and effect has not been proven, most studies were done with cannabis containing THC, and there are no data specific to pure CBD. Guidelines advise caution; do not start without talking to your oncologist. | PMID 30670598, PMID 32872248, PMID 35454955, PMID 38610922, PMID 39737331, PMID 36535195, PMID 40184324, PMID 38478773, PMID 36872397 |
| Tamoxifen | Caution | Tamoxifen: In one case, the active breakdown product of tamoxifen (endoxifen) was found to be lower while the person was taking 40 mg of CBD a day. In a small study of 15 patients taking tamoxifen, about 50 mg a day of THC-free CBD oil lowered endoxifen by 12.6% on average; the researchers did not consider this difference important at this dose, and the effect of higher doses is not known. Do not start without talking to your oncologist. | PMID 33191836, PMID 37543688 |
| Chemotherapy / cancer medicines (general) | Information | Chemotherapy and cancer medicines: Data on interactions between CBD and cancer medicines are very limited. Talk to your oncologist before using it. | PMID 30776990, PMID 38478773 |
| Apixaban (DOAC), Rivaroxaban (DOAC) | Information | DOAC blood thinners: If you take a blood thinner, tell your doctor about CBD. There are no clinical data on interactions between these medicines and CBD; there is only a general warning in the package leaflet. | dailymed.nlm.nih.gov |
To check interactions with the medicines you take: CBD drug interaction checker.
How was CBD used in studies?
There is no evidence-based dose for using CBD as a cancer treatment. In the brain tumor case series with no comparison group, patients used 400–600 mg of CBD a day (study dose; not a personal recommendation). In the study of the spray containing THC and CBD, up to 12 sprays a day (study dose; not a personal recommendation) were used. In the study comparing CBD with placebo in patients with advanced cancer, the median dose chosen by patients was 400 mg a day (study dose; not a personal recommendation), and disease progression or survival did not change. These doses are not evidence of any benefit.
Study details (for health professionals)
Based on current evidence, CBD does not treat cancer, shrink tumors or boost the effect of chemotherapy. In the secondary analysis of the controlled study with pure CBD oil, disease progression and survival did not change. Lab and animal findings have not been confirmed in humans; uncontrolled case series (of 15 and 119 patients) and published case reports carry no evidential value; 81% of 77 published cases were rated as weak evidence for this claim. In a phase 1 safety study with 600–800 mg/day Epidiolex in 21 patients with biochemical recurrence of prostate cancer, PSA stayed stable in most patients; because there was no control group, an anti-tumor effect cannot be considered shown. ASCO 2024: cannabis/cannabinoids should not be used in place of cancer treatment (strong recommendation) and should not be recommended outside of clinical trials to boost the effect of tumor-directed treatment either. In three of six observational studies examining cannabis use in people receiving immunotherapy, worse response or survival was seen, and in three it was not; these studies do not show cause and effect, but ASCO recommends caution in these patients. In observational studies of people who were using or had previously used cannabis when they were diagnosed with cancer, no clear difference was seen in survival, in cancer coming back or in a second cancer developing (in HPV-related oropharyngeal cancer, 47 patients matched with 47; at the same center, among 513 head and neck cancer patients, a second primary cancer occurred in 2 of 59 cannabis users and 23 of 454 non-users; in the matched analysis of a French cohort of 8,999 patients with lung cancer, HR 0.90, 95% CI 0.68–1.18; in 1,472 patients with bladder cancer that had not spread into the muscle layer, recurrence in the first 2 years, HR 0.87, 95% CI 0.56–1.33 in current users); in lung cancer, people who smoked tobacco along with cannabis were diagnosed at a younger age than those who smoked only tobacco, and aggressive tumor types were more common. These studies are observational, cannabis use relies mostly on self-report and the share of tobacco cannot be fully separated; they do not show cause and effect (very low certainty). October 2026 search (PubMed, Cochrane, ClinicalTrials.gov, Europe PMC): only 2 small studies were found that measured a tumor or survival outcome in humans and randomly compared patients receiving cannabinoids with those not receiving them (one a secondary analysis of a symptom study with pure CBD, the other a 21-person safety study with a spray containing THC and CBD); the result of a third, with 122 patients, has not been published. In addition, 1 randomized study comparing two THC:CBD ratios, 3 uncontrolled trials, 2 case series, 10 observational comparisons, 5 observational studies examining the course of the disease in people who were using or had previously used cannabis when they were diagnosed with cancer, 2 systematic reviews (one Cochrane), 1 review assessing published case reports, 1 narrative review and the ASCO guideline were found; all are in the table below.
Evidence assessment: Insufficient: no RCT measuring anti-tumor effect as the primary outcome; the only placebo-controlled data are a secondary analysis of a symptom study (no difference)
CBD alone
Pure CBD has not been shown to have an anti-tumor effect in humans; in the MedCan1 secondary analysis, progression and survival did not change. The prostate cancer phase 1 study and the two case series reporting positive results (15 and 119 patients) are uncontrolled.
Products containing THC
Studies measuring tumor response or survival with THC-containing products are small and mostly safety-focused: the nabiximols + temozolomide phase 1b study in glioblastoma (21 people randomized) was not powered for survival; the 88-patient glioma study had no comparison group without cannabis; in chronic lymphocytic leukemia, a single dose of spray slightly reduced cancer cells in the blood for only a few hours. The result of the 122-patient phase II randomized study (ARISTOCRAT) has not been published as of October 2026. Observational findings on cannabis use in people receiving immunotherapy are conflicting: some show worse response and survival, some show no difference.
Evidence: Very weak: the only randomized data comparing with a no-cannabis group are a small subgroup (21 people) of a phase 1b safety study; observational studies are conflicting; no approval/evidence
Dose range in studies
400–600 mg/day CBD in the uncontrolled glioblastoma series; 600–800 mg/day in the prostate cancer phase 1; up to 12 sprays/day (30 mg CBD + 32.4 mg THC) in the nabiximols phase 1b; median dose chosen by patients 400 mg/day in the pure CBD RCT in advanced cancer; in the glioma study, a single nightly dose averaging about 10 mg THC + 11 mg CBD (1:1) or 27 mg THC + 7 mg CBD (4:1)
Starting dose and titration
Not reported in detail in the studies.
These are doses researchers gave under medical supervision; they are not a recommended dose for you. "mg/kg/day" means milligrams per kilogram of body weight per day.
| Study | Participants | Product | Dose and titration | Duration | Result | Source |
|---|---|---|---|---|---|---|
| O'Leary 2024 (MedCan1 secondary analysis) Secondary analysis of a double-blind, placebo-controlled RCT (MedCan1); the trial was designed for symptom burden | Records of 135 patients reviewed, 128 analyzed (144 randomized in the main trial) Advanced cancer | CBD oil 100 mg/mL (pure CBD) | CBD oil 100 mg/mL; from 0.5 mL (50 mg) once daily up to 2 mL three times daily (600 mg/day); median dose chosen by patients 400 mg/day (main publication) Patients increased the dose themselves (the main trial's schedule) | 56 days of follow-up | Progression in 36% of patients at day 28 and 49% at day 56; no difference between CBD and placebo (day 14 p = 0.33; day 28 p = 0.67; day 56 p = 0.50); no difference in survival (p = 0.38). The trial was not designed to measure anti-tumor effect; treatment 28 days, follow-up 56 days Side effects: In the main trial, side effects similar in the two groups; shortness of breath more common with CBD (Hardy 2023) | PMID 38307703, doi:10.1136/spcare-2023-004746, Main publication: Hardy 2023, PMID 36409969, ANZCTR ACTRN12618001220257 |
| Likar 2021 Retrospective case series, no control group | 15 Glioblastoma, added to standard treatment | Oral CBD | 400–600 mg/day in the abstract; 200–600 mg/day in the cases (e.g., from 2×100 mg to 2×300 mg); additional dronabinol (THC) 7.5 mg/day in 2 cases No standard schedule; case by case | Case by case, months to years (no fixed duration) | Mean survival 24.2 months, median 21 months. Uncontrolled; open to selection bias; causation cannot be established. Survival was calculated from diagnosis, while CBD was started months or years after diagnosis in some patients; most patients received standard treatment at the same time. One of the 4 authors reported being a consultant to the European Industrial Hemp Association (EIHA) and several drug companies Side effects: No side effect data in the article | PMID 35403130, doi:10.21873/cdp.10011, Earlier publication: Likar 2019, PMID 31570484, the 6 glioblastoma patients here are also in that series) |
| Myint 2023 Phase 1, open-label dose escalation and expansion | 21 (7 dose escalation + 14 expansion) Prostate cancer with biochemical recurrence (rising PSA) after local treatment | Epidiolex (pure CBD) | From 600 mg/day to 800 mg/day (once daily) Bayesian dose escalation; tapering over 10 days after 90 days | 90 days | At week 12, PSA stable in 16 of 18 patients, partial decline in 1 (at most 41%), progression in 1; the definition of 'stable' also includes a PSA rise of less than 25%; imaging showed progression in 3 patients (one during the study, two afterward); no control group, no anti-tumor effect shown Side effects: No dose-limiting toxicity; diarrhea 55%, nausea 25%, tiredness 20% (grade 1–2) | PMID 37173971, doi:10.3390/cancers15092505, NCT04428203 |
| Twelves 2021 (glioblastoma) Phase 1b; Part 1 open-label, Part 2 randomized placebo-controlled | 6 + 21 (12 nabiximols / 9 placebo) First recurrence of glioblastoma | Nabiximols + dose-intense temozolomide | 1 spray (evening) → 12 sprays/day (30 mg CBD + 32.4 mg THC) +1 spray per day | ≤12 months | Safety study. Progression-free at 6 months 33% in both arms. 1-year survival 83% vs. 44% (p=0.042); not powered for survival, 2 early deaths in the placebo arm. Did not affect temozolomide PK. During follow-up in Part 2, 5 of 9 patients in the placebo arm and 2 of 12 patients in the nabiximols arm died. Supported by the manufacturer (GW Research); 3 of the 8 authors are employees of the manufacturer and hold stock options Side effects: Vomiting, dizziness, tiredness, nausea, headache; mostly grade 2–3 | PMID 33623076, doi:10.1038/s41416-021-01259-3, NCT01812603, NCT01812616 |
| Guzmán 2006 Phase I pilot | 9 Recurrent glioblastoma | THC into the tumor | THC by catheter into the tumor cavity: 20–40 µg on day 1, increased to 80–180 µg/day over 2–5 days Increased over 2–5 days based on psychoactive side effects | Median cycle 10 days; median total 15 days | Safety-focused; median survival 24 weeks; no control group Side effects: No overt psychoactive effects | PMID 16804518, doi:10.1038/sj.bjc.6603236 |
| ARISTOCRAT (NCT05629702) Phase II, double-blind, placebo-controlled RCT (2:1): temozolomide ± nabiximols in recurrent glioblastoma (University of Birmingham) | 122 enrolled (target 234 in the protocol publication; current target 120 in the ISRCTN registry) MGMT-methylated recurrent glioblastoma | Nabiximols + temozolomide | Nabiximols up to 12 sprays/day + temozolomide (cycle 1 150 mg/m², then 200 mg/m², days 1–5) Self-titrated by the patient during days 1–14 of cycle 1 | 28-day cycles, at most 6 cycles; at least 12 months of follow-up | Enrollment closed on October 7, 2026; completion April 30, 2027 in ISRCTN, primary completion October 7, 2027 on ClinicalTrials.gov (estimated); as of October 2026, no results have been published. The primary outcome is overall survival. The investigator-initiated study is funded by The Brain Tumour Charity; nabiximols and placebo are provided free of charge by the manufacturer (Jazz Pharmaceuticals) | NCT05629702, ISRCTN11460478, protocol: Bhaskaran 2024, PMID 38225549 |
| Abrams 2021 Review (preclinical and clinical) | Cannabinoids | Cell and animal studies have not translated into human results | PMID 34850894, doi:10.1093/jncimonographs/lgab010 | |||
| Schloss 2021 Phase 2, double-blind, randomized; two THC:CBD ratios compared with each other, no placebo (retrospective historical comparison group for secondary outcomes) | 88 enrolled (41 in the 1:1 arm and 42 in the 4:1 arm for at least 4 weeks); 61 people completed 12 weeks Recurrent or inoperable high-grade glioma (90% glioblastoma), added to standard treatment (Australia) | Whole-plant cannabis oil, THC:CBD 1:1 or 4:1 (by mouth, single nightly dose) | Mean tolerated daily dose: about 10.4 mg THC + 10.8 mg CBD in the 1:1 arm; about 27 mg THC + 6.8 mg CBD in the 4:1 arm Starting at 0.2 mL and increasing until tolerated (at most 5 mL in a single dose) | 12 weeks | Primary outcomes tolerability and quality of life: both ratios were tolerated; no difference between ratios in the total quality-of-life score (FACT-Br) (p = 0.90); physical (p = 0.025) and functional (p = 0.014) subscores were better in the 1:1 arm, and sleep improved in both arms. Secondary outcome, tumor (MRI at week 12): shrinkage in 11%, stable disease in 34%, slight increase in 16%, progression in 10%; no difference between the two ratios (the denominators vary between 53 and 61 in the article). The comparison group not taking cannabis comes only from retrospective records (different dexamethasone and surgery rates), and no statistics are given; so no conclusion can be drawn about cannabis's effect on the tumor. The product and funding were provided by FIT-Bioceuticals Side effects: No serious side effects; dry mouth 13%, nighttime tiredness 11%, dizziness 10%, drowsiness 7%; at week 8, mild nighttime hallucinations, paranoia or euphoria in 4 people (6%); dose reduced in 3 people | PMID 34094937, doi:10.3389/fonc.2021.649555, ANZCTR ACTRN12617001287325 |
| Melén 2022 Phase 2, single group, open-label; single dose | 23 Asymptomatic, indolent leukemic B-cell lymphoma (including chronic lymphocytic leukemia) (Sweden, Karolinska) | Mouth spray containing THC and CBD (Sativex), single dose | Single dose; amount not reported in the abstract or in the EU trial registry | Single dose; 24 hours of follow-up | The primary outcome was a decrease in leukemic B cells in the blood: median 11% decrease within 2 hours (p = 0.014), lasting 6 hours and completely gone by 24 hours; no change in cancer cell death (apoptosis) or proliferation; normal B and T cells also decreased. The researchers concluded that THC/CBD has no therapeutic potential in these lymphomas. No control group Side effects: Grade 1–2 side effects in 91% of patients: dry mouth 78%, dizziness (vertigo) 70%, drowsiness 43% | PMID 35037561, doi:10.1080/10428194.2021.2020776, EudraCT 2014-005553-39 (EU Clinical Trials Register: completed, no results section) |
| Kenyon 2018 Retrospective case series (routine records of a private clinic), no control group | 119 Cancer patients with solid tumors (the authors highlight breast cancer and glioma) (United Kingdom) | Pharmaceutical-grade synthetic CBD | Not reported in the abstract (full text could not be accessed) | Records from a four-year period; duration per patient not in the abstract | The authors reported a 'clinical response' in 92% of the 119 cases (in most, a decrease in circulating tumor cells in the blood; in some, shrinkage on scans); how response was defined and how many patients were imaged is not in the abstract. No comparison group. The ASCO 2024 guideline points out that in this series those treated for less than 6 months were excluded and the standard cancer treatment received at the same time by almost all patients was disregarded; therefore it does not show an effect of CBD Side effects: The authors reported that no side effects were seen (how they were collected is not in the abstract) | PMID 30275207, doi:10.21873/anticanres.12924, The same author's breast, prostate and glioma follow-up publications are not in PubMed, assessed in the Guggisberg 2022 row |
| Braun 2024 (ASCO guideline) Clinical practice guideline; based on a systematic review (13 systematic reviews and 5 primary studies; search January 2023) | Adults with cancer | Cannabis and cannabinoids (pure, synthetic and plant-based) | Recommendation 2.1: cannabis or cannabinoids should not be recommended outside of clinical trials to boost the effect of cancer treatment (very low quality of evidence, weak recommendation). Recommendation 2.2: should not be used in place of cancer treatment (consensus-based; very low quality of evidence, strong recommendation). Evidence on anti-tumor effect was found to be limited; caution is recommended in people receiving immunotherapy because of preliminary observational data reporting poor outcomes with cannabis; the guideline also notes that MASCC 2023 does not recommend cannabinoids for any purpose in people receiving checkpoint inhibitors. 2 of the 15 panel members reported ties to cannabinoid companies; the panel also included authors of two studies the guideline relies on (Bar-Sela 2020, Twelves 2021) Side effects: It states that use for the purpose of cancer treatment can lead to significant clinical (tiredness, mental fogginess, feeling high) and financial harm without proven benefit | PMID 38478773, doi:10.1200/JCO.23.02596, Q&A summary: Braun 2024, PMID 38478793 | ||
| McBain 2021 (Cochrane, recurrent glioblastoma) Cochrane systematic review and network meta-analysis (42 studies: 34 RCTs, 8 non-randomized; search December 2019) | 5,236 (whole review); cannabinoid part 21 Glioblastoma that progressed or recurred after standard treatment | The only study with a cannabinoid: mouth spray containing THC and CBD + temozolomide, vs. placebo | In the review comparing treatments for recurrent glioblastoma, there was only one small pilot study with a cannabinoid (21 people; only a conference abstract at that time), and it could not be included in the network meta-analysis. According to the abstract data, median survival about 18.3 vs. 12.3 months, 1-year survival 83% vs. 56% (in favor of the spray); the authors consider this not a conclusion but a finding 'worth further investigation'. In the full text of the same study published later, 1-year survival in the placebo arm was 44% (Twelves 2021 row) | PMID 34559423, doi:10.1002/14651858.CD013579.pub2 | ||
| Rodriguez-Almaraz 2020 (systematic review and meta-analysis) Systematic review and meta-analysis (search November 2018) | 5 studies, 176 patients (2 studies only conference abstracts) Malignant central nervous system tumors in adults (mostly glioma) | Cannabis and cannabinoids (THC, THC and CBD spray, cannabis oil, unspecified cannabis) | No significant difference in 1-year risk of death between cannabis users and non-users (RR 0.46 in the text; 95% CI 0.16–1.31; different numbers in the abstract: RR 1.07; 95% CI 0.14–8.25). Only one of the five studies is randomized (21 people); one examines the incidence of glioma, not survival. The authors' interpretation in the abstract of 'limited, moderate-quality evidence supporting its use as an adjunct treatment' rests on a non-significant result; the authors state that randomized studies are needed Side effects: In the studies reviewed: dizziness, dry mouth, increased appetite, sleepiness and psychoactive effects | PMID 32765889, doi:10.1093/nop/npaa013 | ||
| Guggisberg 2022 (assessment of case reports) Review: all published case reports and clinical data were collected through a PubMed and EBSCO search and graded by strength of evidence | 77 cases (9 case reports or series) Published cases claiming that cannabis treated cancer (breast, brain, prostate, pancreas, etc.) | Mostly CBD oil; THC in a few cases | 81% of the cases were rated weak, 5% moderate and 14% (11 cases) strong evidence; three criteria were required for 'strong': active cancer when cannabis was started, response confirmed by lab tests or imaging, and no other cancer treatment at the same time. Most of the cases come from four publications by a single author (only one of them in PubMed: Kenyon 2018); in 29%, cannabis had been used together with standard cancer treatment. The authors state that the published cases do not support the claim that cannabis is a cancer drug and that it should not be used in place of standard treatment outside of clinical trials | PMID 34370591, doi:10.1089/can.2021.0045 | ||
| Coschi 2025 (CCTG pooled analysis) Observational analysis with individual patient data from four randomized cancer trials (cannabinoid use was not randomly assigned) | 684 (32 people were using cannabinoids at baseline, 65 at any time) Advanced solid tumors receiving durvalumab + tremelimumab (± chemotherapy) (lung, colorectal, pancreatic and other; most cannabinoid users from the lung and pancreatic trials; Canada) | In drug records: cannabis oil, marijuana, dronabinol, nabilone; the authors also counted propacetamol (an acetaminophen prodrug, not a cannabis product) as a cannabinoid | Not reported (dose and THC/CBD ratio not recorded in the trials) | Follow-up period of the trials | Cannabinoid use at baseline was not linked to overall survival (p = 0.35), progression-free survival by the standard criteria (p = 0.12) or best response; progression-free survival by immunotherapy-specific criteria (iRECIST) was longer in users (median 10.9 vs. 8.3 months; adjusted p = 0.05). Few users (32 people at baseline). Propacetamol, an acetaminophen prodrug, was also included in the 'cannabinoid' definition; how many users took propacetamol is in the supplementary tables (could not be read). AstraZeneca provided drug and funding support for the trials; 3 of the 14 authors reported ties to drug companies (including Jazz Pharmaceuticals, which also makes cannabinoid medicines) Side effects: No difference in immune-related side effects (grade 1–2 p = 0.96; grade 3–4 p = 0.65) | PMID 40184324, doi:10.1080/1750743X.2025.2485012, Trials: CCTG BR.34, CO.26, PA.7, IND.226 |
| Waissengrin 2023 Retrospective cohort (consecutive patients); mouse experiment in the same article | 201 (102 licensed for cannabis, 99 not using it) Metastatic non-small cell lung cancer receiving first-line pembrolizumab alone (Israel, Tel Aviv) | Licensed medical cannabis (license in the first month of treatment; product composition not in the abstract) | Not reported (in the abstract) | Time to tumor progression similar (5.6 vs. 6.1 months; p = 0.386). Overall survival numerically shorter in cannabis users (23.6 vs. 54.9 months) but not significant (p = 0.08); in multivariate analysis, cannabis was not an independent factor for death. Cannabis users were younger, mostly women and more often had brain metastases; they had been licensed for pain (71%) and loss of appetite (34%). In the mouse experiment in the same article (in animals), THC did not reduce the effect of the PD-1 drug. 5 of the 8 authors reported fees or grants from drug companies, including immunotherapy makers | PMID 36535195, doi:10.1016/j.ejca.2022.11.022 | |
| Taha 2019 Retrospective observational cohort (single center) | 140 (89 nivolumab alone, 51 nivolumab + cannabis); response analysis in the 116 patients who lived longer than 2 months Advanced melanoma, non-small cell lung cancer and kidney cancer receiving nivolumab (Israel, Rambam) | Medical cannabis licensed in Israel (flower, oil or both; THC and CBD ratios variable) | Mostly 20 g per month (the lowest licensed amount) | Those who started nivolumab between August 2015 and August 2016 | Response rate lower in cannabis users: 15.9% vs. 37.5% (in those who lived longer than 2 months; in multivariate analysis, OR about 3.1; 95% CI 1.24–8.1; p = 0.016); in all patients, adjusted OR 2.74 (p = 0.031). No difference in progression-free and overall survival in multivariate analysis (in univariate analysis, overall survival was shorter in cannabis users: HR 1.58; p = 0.045); THC and CBD ratio did not affect response. An independent reanalysis (Piper 2024) showed that cannabis users were significantly younger and that the share of smokers was numerically higher (57% vs. 40%; p = 0.06); the article had stated that the groups were similar Side effects: No difference between groups in immunotherapy side effects | PMID 30670598, doi:10.1634/theoncologist.2018-0383, Independent reanalysis: Piper 2024, PMID 38610922 |
| Bar-Sela 2020 Prospective observational study (consecutive patients, single center) | 102 (68 immunotherapy alone, 34 immunotherapy + cannabis); the sample size calculation anticipated 243 patients Stage 4 cancer starting checkpoint inhibitors (mostly non-small cell lung cancer and melanoma) (Israel, Rambam) | Medical cannabis licensed in Israel (flower, oil or both), started before immunotherapy | Mostly 20 g per month | Enrollment September 2016–September 2018; at least 7 months of follow-up | The primary outcome (time to tumor progression) was shorter in cannabis users: median 3.4 vs. 13.1 months (HR adjusted for treatment line 1.95; 95% CI 1.17–3.26); overall survival 6.4 vs. 28.5 months (HR 2.18; 95% CI 1.24–3.82). Enrollment was stopped at an interim analysis of 102 patients instead of the planned 243. Cannabis users more often received immunotherapy as a second or later line (76% vs. 54%); smoking data were not given. The baseline table was corrected in 2022. An independent reanalysis (Piper 2024) reported that of the 22 p-values in the corrected table, only 1 could be obtained with the test stated in the article, 17 could be obtained with another test, and 4 could not be obtained at all; that the difference in treatment line was significant with the appropriate test (p = 0.03); and it found percentage errors; because raw data were not available, the main survival results could not be recalculated. The results should therefore be read with caution Side effects: Immune-related side effects less common in cannabis users (e.g., colitis only in non-users, 9%) | PMID 32872248, doi:10.3390/cancers12092447, PMID 35454955, Table 1), independent reanalysis: Piper 2024, PMID 38610922 |
| Hadid 2024 Retrospective cohort (single center) | 105 (28 using cannabis, 77 not using it) Solid tumors receiving checkpoint inhibitors (62% lung cancer) (US, Detroit) | Mostly (82%) dronabinol (synthetic THC); also non-prescription cannabis or CBD | Most users 5–10 mg a day | Those who received immunotherapy for at least 2 months between August 2014 and August 2018; median follow-up 29.2 months | The primary outcome, overall survival, was shorter in cannabis users: median 6.7 vs. 17.3 months (adjusted HR 2.25; 95% CI 1.25–4.05; p = 0.007); progression-free survival 4.8 vs. 9.7 months (adjusted HR 2.21); disease control 11% vs. 38%. Users were younger and 96% had smoked (74% among non-users); smoking is not in the final survival model. Does not show cause and effect | PMID 39737331, doi:10.1177/25151355241309095 |
| Alsavaf 2025 Retrospective cohort (single center) | 201 (47 using marijuana) Recurrent or metastatic head and neck cancer receiving checkpoint inhibitors (pembrolizumab, nivolumab) (US, Ohio) | Marijuana use (medical vs. recreational distinction and product not in the abstract) | Not reported (in the abstract) | Those treated between January 2016 and April 2020 | Marijuana use was not linked to overall survival (HR 0.93; 95% CI 0.58–1.49); smoking and alcohol were not linked either. In the whole group, median survival 12 months, response rate 18%. The study examined marijuana as a lifestyle factor together with smoking and alcohol; whether use was medical or recreational, and when and how much was used, is not in the abstract | PMID 39704258, doi:10.1111/ajco.14135 |
| Peleg Hasson 2024 Retrospective cohort (single center) | 93 (29 using medical cannabis, 64 not using it) Ovarian cancer receiving PARP inhibitor maintenance treatment after response to platinum (Israel, Tel Aviv) | Medical cannabis (product composition not in the abstract) | Not reported (in the abstract) | Those treated between January 2014 and January 2020 | Duration of PARP inhibitor use (12.1 and 9.5 months; p = 0.89) and progression-free survival (20 and 21 months; p = 0.83) similar in the two groups. Overall survival longer in cannabis users in the univariate analysis (129.3 vs. 99 months; p = 0.03) but not significant in the multivariate analysis (p = 0.10). The authors' conclusion: cannabis use is not linked to treatment outcomes | PMID 38242547, doi:10.1136/ijgc-2023-004953 |
| Gastmeier 2024 Retrospective multicenter cohort (legally mandated monitoring records) | 9,419 (those who lived at least 7 days; subgroup 7,085: those who lived 7–100 days); 310 (3.3%) received THC Patients receiving specialized palliative home care (Germany, Brandenburg; the title says 'palliative cancer patients', but the distribution of diagnoses is not given) | Prescription THC (type of preparation not in the abstract) | The last (highest) dose in the records; median 4.7 mg/day Started at a low dose and increased based on effect or tolerability | Patients who died between April 2017 and September 2021 | Longer survival in those taking more than 4.7 mg THC a day (median 40 vs. 25 days in the 7–100-day group; in the large group, HR adjusted for age and sex 0.69; 95% CI 0.59–0.81); no difference at lower doses. 62% of the 310 patients receiving THC were from a single palliative care team (11% among those not receiving THC); the models account for the team difference but do not include disease severity or diagnosis. The authors write that they do not discuss an anti-tumor effect and consider it unlikely in this period, and that they cannot rule out that patients in better condition may have received THC; because the dose is the last value in the records, people who lived longer may end up in the higher-dose group. 3 of the 4 authors reported speaker fees or advisory board membership with cannabis companies Side effects: Not recorded | PMID 38655402, doi:10.1159/000538311 |
| Phansila 2022 Retrospective cohort (6 hospitals) | 491 (87 medical cannabis, 404 standard palliative pain treatment) Newly diagnosed advanced bile duct cancer (cholangiocarcinoma) and liver cancer (Thailand, northeast) | Oral cannabis oil approved in Thailand (dose, composition and duration of use missing from records) | Missing from records | September 2019–June 2021 | Median survival after clinic registration 5.7 months in the cannabis group, 0.8 months in the standard group (HR adjusted for age, sex, treatment and time from diagnosis to registration 0.28; 95% CI 0.20–0.37). Stage, performance status and pain data were not available and could not be included in the analysis; patients in the standard group had been referred to the palliative clinic very late in their illness. The authors note that unmeasured confounding factors could explain the result. Third version in a journal with post-publication peer review | PMID 41113085, doi:10.12688/f1000research.123250.3, F1000Research first version 2022, version 3 October 3, 2025 |
| Gallow 2026 Prospective observational comparison (three groups; groups formed by patients' treatment preference, not randomized) | 90 (30 in each group: chemotherapy alone, cannabis alone, chemotherapy + cannabis) Prostate cancer (no hormone therapy given during the study) (South Africa, Eastern Cape) | Sublingual full-spectrum cannabis oils (THC-dominant, balanced and CBD-dominant) | Median daily 12.5 mg THC and 18 mg CBD | 6 months | The course of PSA differed between groups (p < 0.001): it fell faster in the cannabis groups, but values were similar at month 6. A complete metabolic response on PET/CT was seen only in the cannabis groups (6 patients; chemotherapy + cannabis 16.7%, cannabis alone 3.3%); p = 0.013 in favor of tumor response in the combined group; partial response was the same in the chemotherapy-alone and cannabis-alone groups (30%). Not randomized, groups formed by patients' own preference; the authors also write that the design does not allow conclusions about cause and effect. Cannabis use is based on patients' self-report. 2 of the 5 authors are in the cannabis industry and in a cannabis physicians' association. No independent verification Side effects: Side effects mostly in those receiving chemotherapy; no one left the study | PMID 41939176, doi:10.1159/000550792 |
Reported side effects
- Twelves 2021 (THC-containing): vomiting, dizziness, tiredness, nausea, headache; mostly grade 2–3
- Schloss 2021 and Melén 2022 (THC-containing): dry mouth, dizziness, drowsiness; in the glioma study, mild nighttime hallucinations, paranoia or euphoria in 4 people
- MedCan1 and Myint 2023 (pure CBD): in advanced cancer, side effects similar to placebo, shortness of breath more common with CBD; in prostate cancer with 600–800 mg/day, diarrhea 55%, nausea 25%, tiredness 20% (grade 1–2)
Monitoring done in studies
- Prescription CBD label: liver tests at baseline and at months 1, 3 and 6, then periodically; stop if ALT/AST >3×ULN + bilirubin >2×ULN or transaminases persistently >5×ULN
- INR in people using warfarin
- Drug blood levels in people using everolimus/tacrolimus/sirolimus
Who should be careful
- CBD should not be used in place of cancer treatment (ASCO 2024, recommendation 2.2, strong recommendation)
- Cannabis/cannabinoids are not recommended outside of clinical trials to boost the effect of (tumor-directed) cancer treatment (ASCO 2024, recommendation 2.1, weak recommendation)
- People with liver disease / liver metastases / receiving hepatotoxic treatment: with prescription CBD, ALT >3×ULN 12–13% (placebo 1%), dose-related; in moderate/severe hepatic impairment, the label specifies a low starting dose
- People using warfarin or clopidogrel and those at high risk of bleeding: an interaction mechanism exists (CYP2C9, CYP2C19); no clinical data have been reported that CBD directly increases bleeding risk
- Before surgery/procedures: ASRA 2023 recommends asking about cannabinoid use and including it in the anesthesia plan; the anesthesia team must be told
- People receiving immunotherapy (checkpoint inhibitors): observational studies are conflicting (some show worse response and survival); ASCO 2024 recommends caution, and MASCC 2023 recommends particular attention to possible harms in these patients
- People using everolimus, tacrolimus, sirolimus or oral targeted drugs: should not add it without consulting the oncologist/pharmacist
- Older people, people taking many medicines, those taking sedatives/opioids: somnolence, dizziness, risk of falls; with THC-containing products, confusion and psychotomimetic effects
- Use for tumor 'treatment': uncontrolled case series are not evidence; per ASCO, abandoning standard treatment is strongly recommended against
- Pregnancy/breastfeeding, history of psychiatric illness (with THC-containing products): cancer studies excluded these groups
Drug interactions
- Everolimus: exposure rose ~2.5-fold; label: start everolimus at a low dose, monitor levels (high, human PK data)
- Tacrolimus, sirolimus, digoxin (P-gp substrates): the label states that levels may rise (moderate)
- Oral P-gp substrate chemotherapy/targeted drugs (e.g., many tyrosine kinase inhibitors): theoretical; no human data
- CYP2C19 substrates and prodrugs (clopidogrel): substrate levels rise, and with prodrugs the active metabolite may decrease; no human data for oncology drugs
- Warfarin: case report of raised INR; INR should be monitored
- CYP3A4 substrates (taxanes, irinotecan, docetaxel, many TKIs): in the label, midazolam did not change (approved CBD 750 mg twice daily); a single dose of a CBD-dominant extract (640 mg CBD + 20 mg THC) raised midazolam AUC by 56% (Bansal 2023, PMID 37313955); herbal cannabis tea did not affect the PK of irinotecan and docetaxel (n=24); nabiximols did not affect temozolomide PK; these results cannot be generalized
- Immunotherapy: in cannabis users (mostly THC-containing), nivolumab response rate 15.9% vs. 37.5% (Taha 2019; in the 116 of 140 patients who lived longer than 2 months); in a prospective observational study, shorter time to progression and survival (Bar-Sela 2020, n=102); shorter survival in 28 patients, most using dronabinol (Hadid 2024); on the other hand, no link with survival was found in 201 lung cancer patients receiving pembrolizumab (Waissengrin 2023), in a pooled trial analysis of 684 patients (Coschi 2025) or in 201 head and neck cancer patients (Alsavaf 2025); in two Israeli studies, most of the p-values in the baseline tables could not be obtained with the test stated in the article in an independent reanalysis, and group differences not reported in the articles were found; the main results could not be recalculated because raw data were not available (Piper 2024); causation has not been proven, and there are no data specific to pure CBD
- Opioids: in MedCan1, CBD dose was unrelated to opioid use; no opioid-sparing effect has been shown with THC-containing products; somnolence increases with CNS depressants
- Citalopram/escitalopram: in 6 patients who added CBD (200–800 mg/day), citalopram levels rose significantly (Anderson 2021, PMID 34121064)
- Valproate and liver-toxic drugs (some chemotherapies, methotrexate): no data on use together with hepatotoxic chemotherapies
- Tamoxifen: in one case, endoxifen was found to be low with 40 mg/day CBD (Parihar 2020, PMID 33191836)
- No clinical studies have been reported with direct oral anticoagulants (apixaban, rivaroxaban)
Abbreviations: RCT, randomized controlled trial (a study in which participants are assigned to groups by chance); placebo, an inactive substance; SMD, OR and RR, effect measures used in analyses that pool studies; CYP, liver enzymes that break down medicines.
If you are considering CBD
- Do not use CBD in place of your cancer treatment; expert organizations (e.g., the American Society of Clinical Oncology, ASCO 2024) state as a strong recommendation that standard treatment should not be abandoned.
- If you want to use CBD or any herbal product, talk about it openly with your oncologist; you can assess interactions together.
- This conversation is especially important if you are using immunotherapy, everolimus, tamoxifen or a targeted drug taken by mouth.
- Be careful with products promoted as "curing cancer"; there is no well-designed human study supporting these claims. Reports of positive results come from studies with no comparison group or in which patients were not randomly assigned.
Choose your age group, medicines and situation to prepare a short summary you can take to your doctor. Nothing you enter is sent anywhere.
Bottom line
Looking for hope in the fight against cancer is very understandable. But today there is no well-designed human study showing that CBD treats cancer or shrinks tumors. The safest path is to continue your treatment and talk openly with your care team about anything you are curious about.
Frequently asked questions
Does CBD oil work for cancer treatment?
Research to date does not support this; CBD has not been shown to shrink tumors or treat cancer in humans. In patients with advanced cancer, pure CBD oil did not change disease progression or survival compared with an inactive drug (placebo).
What do the positive results from lab studies mean?
Cell and animal studies show researchers which questions to ask, but they are not proof that something will work in humans. Lab findings on CBD have not been confirmed in human studies so far.
Does CBD boost the effect of chemotherapy?
There is no human study showing this. On the contrary, CBD can change the levels of some cancer medicines in the body. That is why, if you are considering CBD during treatment, be sure to consult your oncologist.
Can I use CBD while receiving immunotherapy?
In some observational studies, patients using cannabis, mostly THC-containing, had a worse response to immunotherapy or worse survival; other studies found no difference. It has not been proven that this was caused by cannabis, and there are no data specific to pure CBD; but because of this uncertainty, it is important not to use it without talking to your oncologist.
Are the stories of cancer being cured with CBD true?
Stories like these and case series with no comparison group do not count as evidence; it is not possible to separate out the role of other treatments received in the same period and of the disease's own course. In a review of 77 published case reports, 81% of the cases were judged insufficient to support this claim; in 29% of the cases, cannabis had been used together with standard cancer treatment.
Can CBD oil for cancer treatment be obtained with a prescription in Turkey?
In Turkey, products derived from cannabis are regulated by the Kenevirden Elde Edilen Ürünlere Dair Yönetmelik (Regulation on Products Derived from Hemp) dated January 31, 2026. These products, including CBD, can be sold only in pharmacies. Those in the medicine and health product category are dispensed with a prescription; the regulation does not state a prescription requirement for supplement products and cosmetics with a THC content of at most 0.3%. As of October 2026, there is no approved CBD medicine in Turkey. If you are thinking of using it, talk to your doctor first.
I saw a study saying there is a “scientific consensus” that cannabis is good for cancer; is that true?
A study published in 2025 that describes itself as a meta-analysis used a computer program to count words meaning “supports”, “does not support” or “unclear” in the text of more than 10,000 articles on cannabis (sentiment analysis). Because words meaning support appeared more often, it concluded that there is a consensus on the benefit of cannabis in cancer. This method does not measure how patients are affected: the publication does not pool the results of studies done with patients (such as tumor shrinkage or survival), and a word appearing often in articles does not show that a treatment works. The authors themselves also state that this kind of word analysis will inevitably contain errors and that the findings cannot be used to predict with certainty the effect of a treatment or whether it works. For this reason, this study does not count as evidence of a treatment and is not in the table below. In studies in which patients were assigned to groups by lottery and the tumor or survival was measured directly, it has not been shown to date that CBD or cannabis treats cancer (insufficient evidence); the American Society of Clinical Oncology (ASCO 2024) recommends that cannabis products not be used in place of cancer treatment.
References
Show 24 references
- O'Leary 2024 (MedCan1 secondary analysis). Secondary analysis of a double-blind, placebo-controlled RCT (MedCan1); the trial was designed for symptom burden. PMID 38307703, doi:10.1136/spcare-2023-004746, Main publication: Hardy 2023, PMID 36409969, ANZCTR ACTRN12618001220257
- Likar 2021. Retrospective case series, no control group. PMID 35403130, doi:10.21873/cdp.10011, Earlier publication: Likar 2019, PMID 31570484, the 6 glioblastoma patients here are also in that series)
- Myint 2023. Phase 1, open-label dose escalation and expansion. PMID 37173971, doi:10.3390/cancers15092505, NCT04428203
- Twelves 2021 (glioblastoma). Phase 1b; Part 1 open-label, Part 2 randomized placebo-controlled. PMID 33623076, doi:10.1038/s41416-021-01259-3, NCT01812603, NCT01812616
- Guzmán 2006. Phase I pilot. PMID 16804518, doi:10.1038/sj.bjc.6603236
- ARISTOCRAT (NCT05629702). Phase II, double-blind, placebo-controlled RCT (2:1): temozolomide ± nabiximols in recurrent glioblastoma (University of Birmingham). NCT05629702, ISRCTN11460478, protocol: Bhaskaran 2024, PMID 38225549
- Abrams 2021. Review (preclinical and clinical). PMID 34850894, doi:10.1093/jncimonographs/lgab010
- Schloss 2021. Phase 2, double-blind, randomized; two THC:CBD ratios compared with each other, no placebo (retrospective historical comparison group for secondary outcomes). PMID 34094937, doi:10.3389/fonc.2021.649555, ANZCTR ACTRN12617001287325
- Melén 2022. Phase 2, single group, open-label; single dose. PMID 35037561, doi:10.1080/10428194.2021.2020776, EudraCT 2014-005553-39 (EU Clinical Trials Register: completed, no results section)
- Kenyon 2018. Retrospective case series (routine records of a private clinic), no control group. PMID 30275207, doi:10.21873/anticanres.12924, The same author's breast, prostate and glioma follow-up publications are not in PubMed, assessed in the Guggisberg 2022 row
- Braun 2024 (ASCO guideline). Clinical practice guideline; based on a systematic review (13 systematic reviews and 5 primary studies; search January 2023). PMID 38478773, doi:10.1200/JCO.23.02596, Q&A summary: Braun 2024, PMID 38478793
- McBain 2021 (Cochrane, recurrent glioblastoma). Cochrane systematic review and network meta-analysis (42 studies: 34 RCTs, 8 non-randomized; search December 2019). PMID 34559423, doi:10.1002/14651858.CD013579.pub2
- Rodriguez-Almaraz 2020 (systematic review and meta-analysis). Systematic review and meta-analysis (search November 2018). PMID 32765889, doi:10.1093/nop/npaa013
- Guggisberg 2022 (assessment of case reports). Review: all published case reports and clinical data were collected through a PubMed and EBSCO search and graded by strength of evidence. PMID 34370591, doi:10.1089/can.2021.0045
- Coschi 2025 (CCTG pooled analysis). Observational analysis with individual patient data from four randomized cancer trials (cannabinoid use was not randomly assigned). PMID 40184324, doi:10.1080/1750743X.2025.2485012, Trials: CCTG BR.34, CO.26, PA.7, IND.226
- Waissengrin 2023. Retrospective cohort (consecutive patients); mouse experiment in the same article. PMID 36535195, doi:10.1016/j.ejca.2022.11.022
- Taha 2019. Retrospective observational cohort (single center). PMID 30670598, doi:10.1634/theoncologist.2018-0383, Independent reanalysis: Piper 2024, PMID 38610922
- Bar-Sela 2020. Prospective observational study (consecutive patients, single center). PMID 32872248, doi:10.3390/cancers12092447, PMID 35454955, Table 1), independent reanalysis: Piper 2024, PMID 38610922
- Hadid 2024. Retrospective cohort (single center). PMID 39737331, doi:10.1177/25151355241309095
- Alsavaf 2025. Retrospective cohort (single center). PMID 39704258, doi:10.1111/ajco.14135
- Peleg Hasson 2024. Retrospective cohort (single center). PMID 38242547, doi:10.1136/ijgc-2023-004953
- Gastmeier 2024. Retrospective multicenter cohort (legally mandated monitoring records). PMID 38655402, doi:10.1159/000538311
- Phansila 2022. Retrospective cohort (6 hospitals). PMID 41113085, doi:10.12688/f1000research.123250.3, F1000Research first version 2022, version 3 October 3, 2025
- Gallow 2026. Prospective observational comparison (three groups; groups formed by patients' treatment preference, not randomized). PMID 41939176, doi:10.1159/000550792
Points that could not be verified from the full text
- ARISTOCRAT (phase II, 122 patients) results are awaited; completion 2027 (ISRCTN April 30, 2027, ClinicalTrials.gov October 7, 2027, estimated); as of October 2026, no results have been published
- The phase 1b study in Spain in which a mixture of THC and CBD was tried together with radiotherapy and temozolomide in newly diagnosed glioblastoma (NCT03529448, 33 patients) was completed in November 2025; as of October 2026, its results are neither in the registry nor in a peer-reviewed publication. The records of two registered studies testing pure CBD alone or as an add-on to standard treatment (NCT02255292, NCT03607643) have not been updated since 2014 and 2018; no results.
- According to the registries, two small studies measuring the effect on tumors are enrolling patients: a cannabis oil containing THC and CBD in untreatable liver cancer (NCT06518434, Netherlands, 20 patients; record not updated since July 2024) and pure CBD vs. placebo before surgery in breast cancer (NCT06148038, US, 84 patients). As of October 2026, no results.
- The full text of the 119-patient synthetic CBD case series (Kenyon 2018) could not be accessed; how response was defined and the dose information were taken from the abstract and from sources assessing this series (ASCO 2024, Guggisberg 2022).
- A short report examining the link between cannabis use disorder and death in patients with colon cancer (Cuomo 2025) was published without an abstract, and its full text could not be accessed; because its result could not be read from the primary source, it is not reported on this page. In the same research group's larger study looking at the records of 22,763 cancer patients (Khoyilar 2025), cannabis dependence was not significantly associated with death; but the abstract does not give the number of patients with cannabis dependence or the size of the effect, the authors note that this group was small, and the full text could not be accessed either. For this reason, neither was included in the table as of October 2026.
Research history
Here we record what changed on this page, when and why, with dates. The newest change is at the top.
The evidence level text now uses the same level name as the top of the page; the level and the result did not change.
The last sentence of the page's short summary was rewritten in calmer, more guiding language: instead of "Talk to your doctor before you start.", it now says who you can talk with, and about what, if you are considering CBD. The result and the strength of evidence did not change.
Five observational studies (head and neck, lung and bladder cancer) looking at the course of the disease in people who were using or had previously used cannabis when they were diagnosed with cancer were added to the table, and a separate paragraph describing them was written in the “What does the research say?” section: no clear difference was seen in survival, in cancer coming back or in a second cancer developing; in lung cancer, aggressive tumor types were more common in people who smoked tobacco along with cannabis. Because these studies are observational, they do not show cause and effect, and the strength of evidence is very weak. For a 2025 publication claiming that there is a “scientific consensus” that cannabis is good for cancer, a question and answer was added explaining what it did and why it does not count as evidence of a treatment. Because the result of a short report on cannabis use disorder and death in colon cancer could not be read, and the abstract of the same research group's larger study gives no figures for cannabis either, both are described under unverifiable items. The result and the strength of evidence did not change.
Related studies: (PMID 31477184, doi:10.1186/s40463-019-0365-4); (PMID 40393352, doi:10.1016/j.resmer.2025.101174); (PMID 41005696, doi:10.1016/j.chest.2025.09.017); (PMID 36449286, doi:10.1001/jamanetworkopen.2022.44430); (PMID 33329979, doi:10.7759/cureus.11483)
Older changes (6)
Display fix: internal working file names left in the text were removed; content and evidence did not change.
In October 2026, PubMed, Cochrane, ClinicalTrials.gov and Europe PMC were systematically searched; 17 studies were added: 2 clinical studies with products containing THC and CBD (glioma and chronic lymphocytic leukemia), a 119-patient pure CBD case series, the ASCO 2024 guideline, 3 reviews (one Cochrane) and 10 observational studies comparing cancer patients who use and do not use cannabis (6 in people receiving immunotherapy; results conflicting). The case series and observational studies reporting positive results were written up together with their methodological limitations and the authors' company ties. Registry numbers, the main publication, doses, death counts and company ties were added to existing rows; ARISTOCRAT's target number of patients was corrected according to verified sources. The texts on immunotherapy were balanced to also show the studies that found no difference, and the warning from the MASCC 2023 guideline was added; statements saying 'no human study' that conflicted with the table were corrected to 'no well-designed human study'; time-dependent statements were written with dates; a transparency sentence was added to the evidence summary. The conclusion and the strength of evidence did not change.
Related studies: Schloss 2021, published May 21, 2021 (PMID 34094937, doi:10.3389/fonc.2021.649555, ANZCTR ACTRN12617001287325); Melén 2022, published June 2022 (PMID 35037561, doi:10.1080/10428194.2021.2020776, EudraCT 2014-005553-39 (EU Clinical Trials Register: completed, no results section)); Kenyon 2018, published October 2018 (PMID 30275207, doi:10.21873/anticanres.12924, The same author's breast, prostate and glioma follow-up publications are not in PubMed, assessed in the Guggisberg 2022 row); Braun 2024 (ASCO guideline), published May 1, 2024 (PMID 38478773, doi:10.1200/JCO.23.02596, Q&A summary: Braun 2024, PMID 38478793); McBain 2021 (Cochrane, recurrent glioblastoma), published May 4, 2021 (PMID 34559423, doi:10.1002/14651858.CD013579.pub2); Rodriguez-Almaraz 2020 (systematic review and meta-analysis), published July 2020 (PMID 32765889, doi:10.1093/nop/npaa013); Guggisberg 2022 (assessment of case reports), published February 2022 (PMID 34370591, doi:10.1089/can.2021.0045); Coschi 2025 (CCTG pooled analysis), published March 2025 (PMID 40184324, doi:10.1080/1750743X.2025.2485012, Trials: CCTG BR.34, CO.26, PA.7, IND.226); Waissengrin 2023, published February 2023 (PMID 36535195, doi:10.1016/j.ejca.2022.11.022); Taha 2019, published April 2019 (PMID 30670598, doi:10.1634/theoncologist.2018-0383, Independent reanalysis: Piper 2024, PMID 38610922); Bar-Sela 2020, published August 28, 2020 (PMID 32872248, doi:10.3390/cancers12092447, PMID 35454955, Table 1), independent reanalysis: Piper 2024, PMID 38610922); Hadid 2024, published December 2024 (PMID 39737331, doi:10.1177/25151355241309095); Alsavaf 2025, published October 2025 (PMID 39704258, doi:10.1111/ajco.14135); Peleg Hasson 2024, published April 1, 2024 (PMID 38242547, doi:10.1136/ijgc-2023-004953); Gastmeier 2024, published March 14, 2024 (PMID 38655402, doi:10.1159/000538311); Phansila 2022, published October 3, 2025 (version 3) (PMID 41113085, doi:10.12688/f1000research.123250.3, F1000Research first version 2022, version 3 October 3, 2025); Gallow 2026, published March 13, 2026 (PMID 41939176, doi:10.1159/000550792)
The names of the finding labels were simplified: the "No benefit seen" label on this page became "No effect found". The assessment did not change.
PubMed and ClinicalTrials.gov were searched for newly published and previously missed clinical studies. Study added: Myint 2023. The conclusion and the strength of evidence did not change.
Related studies: Myint 2023, published April 27, 2023 (PMID 37173971, doi:10.3390/cancers15092505, NCT04428203)
The full texts of the studies were reread and the information on the page was checked against its sources. Corrected: duration, dose, dose titration and side effect details in the study table; drug interaction notes; the "Who should be careful" list; the evidence summary; the finding for THC-containing products. Points that could not be verified from the full text went down from 4 items to 1. The conclusion and the strength of evidence did not change.
Page published. This first assessment reviewed 6 studies.