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CBD drug interaction · Medicine group

Does CBD interact with medicines used in cancer treatment?

Prepared by: cbd.school editorial teamLast reviewed: 5 medicines, 4 warnings24 sources

Cancer treatment uses very different medicines, such as hormone therapies (tamoxifen, enzalutamide), chemotherapy, immunotherapy and mitotane; some of them are processed by the same liver enzymes that CBD uses. On this page you will find how CBD may interact with these medicines, what research and guidelines say, and what you should discuss with your oncologist.

What's on this page?7 sections

Medicines and the importance of their interactions

From peer-reviewed publications and drug labels: the warnings, most important first. The same warnings also appear in the interaction checker. A medicine that is not listed can still interact with CBD.

Cancer medicines: CBD interaction warnings
MedicineImportanceWarningSource
TamoxifenCautionTamoxifen: 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
Immunotherapy (checkpoint inhibitors, e.g., nivolumab)CautionImmunotherapy (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
Enzalutamide, MitotaneCautionStrong enzyme inducers: These medicines can lower the level of CBD in the blood: with rifampin it fell by about one third. There are no direct measurements with others such as carbamazepine; the prescribing information expects a similar drop. Tell your doctor.DailyMed Epidiolex label 7.1, EMA Epidyolex SmPC 4.5
Chemotherapy / cancer medicines (general)InformationChemotherapy 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

How does the interaction happen?

CBD is broken down in the liver mainly by the CYP3A4 and CYP2C19 enzymes. Studies with approved CBD showed that CBD slows some enzymes (CYP2C19, CYP1A2, UGT1A9) and can affect the P-gp transporter in the intestine. Because many cancer medicines are also processed through these pathways, interactions are possible; however, there are very few human studies with cancer medicines, and most of the information rests on laboratory data. (EMA Epidyolex prescribing information 4.5 and 5.2, FDA Epidiolex label §7.2 and §12.3 (05/2026), PMID 30776990, PMID 38478773)

Tamoxifen is a prodrug: much of its effect comes from a breakdown product called endoxifen, formed in the body mostly by the CYP2D6 and CYP3A4 enzymes. It is thought that CBD may lower endoxifen levels by slowing these enzymes. (PMID 37543688, PMID 33191836, Tamoxifen prescribing information)

Enzalutamide and mitotane strongly speed up CYP3A4, the enzyme that breaks down CBD; enzalutamide also moderately speeds up CYP2C19. Rifampin (rifampin), an enzyme inducer of similar strength, lowered the blood level of approved CBD by about a third and its active breakdown product 7-OH-CBD by about 60%. The European product information writes that enzalutamide and mitotane may also cause a similar fall and that CBD's effect may be reduced. (EMA Epidyolex prescribing information 4.5, FDA Epidiolex label §7.1 and §12.3 (05/2026), Enzalutamide (Xtandi) prescribing information §7.2, Mitotane (Lysodren) prescribing information §7.2)

With immunotherapy, the interaction is thought to work not through drug levels but through the immune system: cannabinoids may suppress the activity of immune cells such as T cells. The results of animal studies also conflict: in one, THC reduced the effect of PD-1 therapy; in another, it did not. How much this matters in humans is not known. (PMID 38478773, PMID 36535195)

What do studies and official drug information say?

Each finding shows the type of evidence it rests on. A case report describes a single patient; it does not prove cause and effect.

  1. Observational study

    Immunotherapy: response was lower in people receiving nivolumab (2019)

    The records of 140 patients with advanced cancer (melanoma, lung and kidney cancer) treated with nivolumab were reviewed; 51 were using medical cannabis. The response rate to treatment was 15.9% in cannabis users and 37.5% in non-users. Time without disease progression and overall survival, however, did not differ between the two groups; the THC and CBD ratio of the cannabis did not affect response.

    Source: PMID 30670598

  2. Observational study

    Immunotherapy: survival was shorter in cannabis users (2020)

    Of 102 patients starting immunotherapy, 34 were using cannabis; most were smoking or vaporizing cannabis flower. In cannabis users, the median time to disease progression was 3.4 months (13.1 months in non-users) and median survival 6.4 months (28.5 months); side effects related to immunotherapy, however, were fewer. A correction to this study was published in 2022, and independent researchers reported that most of the statistics could not be verified and that confounding factors such as smoking were not taken into account.

    Source: PMID 32872248, PMID 35454955, PMID 38610922, PMID 40940851

  3. Observational study

    Immunotherapy: outcomes were worse in patients mostly using dronabinol (THC) (2024)

    Of 106 patients receiving immunotherapy at a single center, 28 were using a cannabis product; 82% of them were taking dronabinol (synthetic THC). Median survival was 6.7 months in users and 17.3 months in non-users; time without disease progression was 4.8 and 9.7 months. The authors stated that this possible interaction needs to be investigated in prospective studies.

    Source: PMID 39737331

  4. Observational study

    Immunotherapy: no difference found in other studies (2023, 2025)

    Half of 201 lung cancer patients receiving first-line pembrolizumab were using medical cannabis; the time to disease progression was similar in the two groups. Overall survival was numerically longer in those not using cannabis, but the difference was not statistically significant, and cannabis did not turn out to be an independent factor raising the risk of death; the authors attributed the difference to more severe disease in cannabis users. In pooled data from 684 patients in four clinical trials, using cannabinoids at baseline also did not worsen survival with dual immunotherapy.

    Source: PMID 36535195, PMID 40184324

  5. Guideline

    Guidelines: caution with immunotherapy (2023, 2024)

    The ASCO guideline, noting that the data are preliminary, asks that patients who use or are thinking of using cannabis or cannabinoids while receiving immunotherapy be advised to be cautious. The MASCC guideline also asks that possible harms be carefully weighed in people with cancer, especially those receiving checkpoint inhibitors.

    Source: PMID 38478773, PMID 36872397

  6. Case report

    Tamoxifen: endoxifen rose when CBD was stopped (2022)

    A 58-year-old woman who had had cancer in both breasts, whose disease was in remission and who had been taking tamoxifen preventively for more than 6 years, was using 40 mg of CBD a day for pain after surgery. After CBD was stopped for 60 days, her endoxifen level rose by 18.75% and her N-desmethyltamoxifen level by 9.24%. The authors stated that people taking tamoxifen together with CBD should be monitored for treatment response.

    Source: PMID 33191836

  7. Drug-level study

    Tamoxifen: endoxifen fell by 12.6% in 15 patients (2023)

    Women taking tamoxifen who complained of side effects used about 50 mg a day of THC-free CBD oil under the tongue for four weeks. In the 15 patients measured, the total amount of endoxifen in the blood fell by an average of 12.6% and its lowest level by 18%; the level of tamoxifen itself did not change. The fall stayed within the equivalence limits the researchers had set in advance, and the authors did not consider it important at this dose. The effect of higher doses is not known; the study was single-arm and open-label.

    Source: PMID 37543688

  8. Drug-level study

    Chemotherapy: drug levels did not change in the few studies

    There are very few human data on CBD interactions with cancer medicines. In 24 patients receiving chemotherapy, medical cannabis tea taken for 15 days did not change the blood levels of irinotecan and docetaxel; a mouth spray containing THC and CBD also did not affect temozolomide levels. These studies were not done with pure CBD; the ASCO guideline states that the results cannot be generalized to other products and other cancer medicines.

    Source: PMID 17405893, PMID 33623076, PMID 38478773, PMID 30776990

  9. Official drug information

    Enzalutamide and mitotane: may lower CBD levels

    There is no study looking at these two medicines together with CBD. Based on the fall seen with rifampin, the European product information writes that enzalutamide and mitotane may also lower the levels of CBD and its active breakdown product to a similar degree. The US product information states that increasing the dose of approved CBD may be considered with strong enzyme inducers; the doctor who prescribed the medicine makes this decision. There may also be an effect in the opposite direction: enzalutamide is broken down by CYP2C8 and CYP3A4, and its active breakdown product is formed largely by CYP2C8. The product information for approved CBD writes that CBD may slow CYP2C8 and recommends considering a dose reduction of a medicine broken down by this enzyme if side effects occur; this warning rests on laboratory data, and its importance for enzalutamide is not known.

    Source: EMA Epidyolex prescribing information 4.5, FDA Epidiolex label §7.1, §7.2 and §12.3 (05/2026), Enzalutamide (Xtandi) prescribing information §7.1 and §12.3

  10. Official drug information

    Everolimus is also a cancer medicine

    The level of everolimus, which is used in breast cancer, kidney cancer and neuroendocrine tumors, rose about 2.5-fold with approved CBD. Everolimus's product information recommends a dose reduction with approved CBD in cancer treatment too. Details are on the everolimus and sirolimus page.

    Source: PMID 37132402, Everolimus (Afinitor) prescribing information §2.11 and §7.1

What is monitored?

What to tell your doctor

  • That you use CBD or another cannabis product or are thinking of starting one. The US National Cancer Institute recommends that people with cancer who are considering complementary and alternative therapies discuss this decision, as with any treatment, with their doctors, nurses or pharmacists; the ASCO guideline also asks doctors to ask every patient about cannabis use regularly and without judgment. (NCI PDQ Cannabis and Cannabinoids patient information, PMID 38478773)
  • The type of product (oil, capsule, spray, flower, edible), whether it contains THC, how much and how often you use it, and why you use it (for example, pain, nausea or sleep). (PMID 38478773, NIH NCCIH)
  • To remind them about CBD again whenever your treatment changes, especially when starting immunotherapy, tamoxifen, enzalutamide or mitotane. The patient information for enzalutamide and mitotane asks you to report everything you take, including herbal products. (Enzalutamide (Xtandi) patient information, Mitotane (Lysodren) patient information, PMID 38478773)

If you are not sure whom to ask: Thinking about CBD? Which specialist should you see?

Frequently asked questions

Can I use CBD while receiving chemotherapy?

Make this decision together with your oncologist. There are very few human data on CBD interactions with chemotherapy medicines; in the few studies, cannabis products did not change the levels of some chemotherapy medicines, but these results cannot be generalized to other medicines and products. A lack of data does not mean it is safe.

Does using CBD while receiving immunotherapy reduce the treatment's effect?

It is not known. In some observational studies, response or survival was worse in people who used cannabis; in others, there was no difference; these studies were mostly done with cannabis containing THC, and there is no study looking at pure CBD. The ASCO guideline advises caution for people receiving immunotherapy; do not start without asking your oncologist.

I take tamoxifen; will CBD reduce my medicine's effect?

The effect may be small, but it is not fully known. In 15 patients using about 50 mg of CBD oil a day, endoxifen, tamoxifen's active breakdown product, fell by an average of 12.6%, and the researchers did not consider this difference important at this dose. In one case, endoxifen rose when CBD was stopped. The effect of higher doses is not known; talk to your oncologist.

Does CBD treat cancer?

No; CBD has not been shown to treat cancer. The ASCO guideline recommends that cannabis and cannabinoids not be used as a cancer treatment outside clinical research, and never in place of treatment. You can find details on the cancer treatment and CBD page.

I take enzalutamide for prostate cancer; will it affect CBD?

It may. Because enzalutamide speeds up the enzymes that break down CBD, it may lower CBD's blood level; this information rests on a study with a similar medicine (rifampin) and on the European product information. There is no study looking at enzalutamide together with CBD. Tell your doctor about CBD.

References

Show 24 references
  1. Braun IM et al. Cannabis and Cannabinoids in Adults With Cancer: ASCO Guideline. J Clin Oncol. 2024;42(13):1575–1593. PMID 38478773
  2. To J et al. MASCC guideline: cannabis for cancer-related pain and risk of harms and adverse events. Support Care Cancer. 2023;31(4):202. PMID 36872397
  3. Taha T et al. Cannabis Impacts Tumor Response Rate to Nivolumab in Patients with Advanced Malignancies. Oncologist. 2019;24(4):549–554. PMID 30670598
  4. Bar-Sela G et al. Cannabis Consumption Used by Cancer Patients during Immunotherapy Correlates with Poor Clinical Outcome. Cancers (Basel). 2020;12(9):2447. PMID 32872248
  5. Bar-Sela G et al. Correction: Cannabis Consumption Used by Cancer Patients during Immunotherapy Correlates with Poor Clinical Outcome. Cancers (Basel). 2022;14(8):1957. PMID 35454955
  6. Piper BJ et al. Immunotherapy and Cannabis: A Harmful Drug Interaction or Reefer Madness? Cancers (Basel). 2024;16(7):1245. PMID 38610922
  7. Piper BJ et al. Comment on Bar-Sela et al. Cannabis Consumption Used by Cancer Patients During Immunotherapy Correlates with Poor Clinical Outcome. Cancers (Basel). 2025;17(17):2754. PMID 40940851
  8. Hadid T et al. Association between cannabis use and clinical outcomes in patients with solid malignancies receiving immune checkpoint inhibitors. Ther Adv Vaccines Immunother. 2024;12:25151355241309095. PMID 39737331
  9. Waissengrin B et al. The use of medical cannabis concomitantly with immune checkpoint inhibitors in non-small cell lung cancer: A sigh of relief? Eur J Cancer. 2023;180:52–61. PMID 36535195
  10. Coschi CH et al. Effects of cannabinoids on immune checkpoint inhibitor response: CCTG pooled analysis of individual patient data. Immunotherapy. 2025;17(4):257–268. PMID 40184324
  11. Parihar V et al. Reduction in Tamoxifen Metabolites Endoxifen and N-desmethyltamoxifen With Chronic Administration of Low Dose Cannabidiol: A CYP3A4 and CYP2D6 Drug Interaction. J Pharm Pract. 2022;35(2):322–326. PMID 33191836
  12. Buijs SM et al. CBD-oil as a potential solution in case of severe tamoxifen-related side effects. NPJ Breast Cancer. 2023;9(1):63. PMID 37543688
  13. Engels FK et al. Medicinal cannabis does not influence the clinical pharmacokinetics of irinotecan and docetaxel. Oncologist. 2007;12(3):291–300. PMID 17405893
  14. Twelves C et al. A phase 1b randomised, placebo-controlled trial of nabiximols cannabinoid oromucosal spray with temozolomide in patients with recurrent glioblastoma. Br J Cancer. 2021;124(8):1379–1387. PMID 33623076
  15. Opitz BJ, Ostroff ML, Whitman AC. The Potential Clinical Implications and Importance of Drug Interactions Between Anticancer Agents and Cannabidiol in Patients With Cancer. J Pharm Pract. 2020;33(4):506–512. PMID 30776990
  16. Wray L et al. Pharmacokinetic Drug-Drug Interaction With Coadministration of Cannabidiol and Everolimus in a Phase 1 Healthy Volunteer Trial. Clin Pharmacol Drug Dev. 2023;12(9):911–919. PMID 37132402
  17. FDA: Epidiolex (cannabidiol) prescribing information, section 7.1, 7.2 and 12.3 (05/2026), DailyMed. dailymed.nlm.nih.gov
  18. EMA: Epidyolex prescribing information, section 4.5 and 5.2. www.ema.europa.eu
  19. Enzalutamide (Xtandi) prescribing information and patient information, section 7.1, 7.2 and 12.3 (DailyMed, 08/2026). dailymed.nlm.nih.gov
  20. Mitotane (Lysodren) prescribing information and patient information, section 7.2 (DailyMed, 08/2026). dailymed.nlm.nih.gov
  21. Tamoxifen sitrat tabletsi prescribing information, clinical pharmacology (DailyMed, 08/2026). dailymed.nlm.nih.gov
  22. Everolimus (Afinitor) prescribing information, section 2.8, 2.11 and 7.1 (06/2026), DailyMed. dailymed.nlm.nih.gov
  23. NCI PDQ: Cannabis and Cannabinoids (PDQ) Patient Version (08/2023). www.cancer.gov
  24. NIH NCCIH: Cannabis (Marijuana) and Cannabinoids: What You Need To Know. www.nccih.nih.gov

Last reviewed: . On this date, each source was opened and checked against the related sentence.