What does the research say?
In studies on movement symptoms, pain and thinking skills, patients were split into two groups by chance; one group took products rich in CBD that also contained a small amount of THC, and the other took an inactive pill (placebo). In a 61-person study there was no difference in movement symptoms; for sleep and thinking skills, the results favored placebo. In a 101-person study of people with painful Parkinson’s, no difference was seen in pain or other non-movement symptoms. In another 40-person study, quality of life was better in the placebo group. Cannabis extract capsules containing more THC than CBD did not reduce involuntary movements caused by the medicine levodopa (dyskinesia) in a 19-patient study; side effects were more common in this group.
In a small 21-person study with pure CBD, no difference was seen in movement symptoms; a borderline difference in quality-of-life score was reported in the high-dose group. In a laboratory study with 24 patients, a single dose of pure CBD reduced anxiety triggered by a speaking test and reduced the severity of tremor. But this was a one-time test; it does not count as evidence for daily use. In 33 Parkinson’s patients with REM sleep behavior disorder, in which dreams are acted out during sleep with movements such as shouting or kicking, 14 weeks of pure CBD (75–300 mg a day) did not reduce these episodes differently from placebo; only a temporary increase in sleep satisfaction lasting a few weeks was seen. In a study in 13 patients with marked tremor that tried a very high dose (20–25 mg per kilogram of body weight a day), movement scores improved; but there was no comparison group and the tremor score did not change clearly (this result appears only on the study’s registry page and was not tested statistically). Diarrhea and sleepiness were very common, and liver enzymes rose in 5 people.
For psychosis related to Parkinson’s (symptoms such as seeing or hearing things that are not really there), there is only one 6-patient study without a comparison group. A reduction in symptoms was reported, but data at this level are not enough for a firm conclusion.
Two small studies were done with nabilone, a synthetic drug similar to THC. In a 7-patient study, nabilone given before a levodopa test reduced levodopa-related involuntary movements. In a 38-patient study, people who responded to the drug were selected first; over 4 weeks, non-movement symptoms (especially anxiety and night-time sleep) worsened less in those taking nabilone than in those taking placebo. In a 6-month open extension study with 22 people who completed this study, the improvement in sleep and pain continued; the improvement in the total non-movement symptom score, however, was borderline, and there was no comparison group. In a 22-person study with smoked marijuana, movement scores improved 30 minutes later; but because no placebo was used, it is not known how much of this came from expectation. In 50 patients who started medical marijuana at doses they adjusted themselves, improvement in sleep, pain and getting up at night to urinate was reported after 3 months; in the records of 69 patients given medical marijuana (mostly drops containing equal amounts of THC and CBD) at a neurology center in the US, improvement in at least one symptom was also noted in most patients. Neither of these two studies had a comparison group. In a retrospective study comparing 76 patients using medical marijuana with similar patients not using it over 1–3 years, no worsening was seen in disease progression or mental health symptoms. All of these studies are small and most are uncontrolled; for THC-containing products and nabilone, the strength of evidence is weak.
The most recent meta-analysis pooling these studies (2026) concluded that cannabinoids do not significantly improve movement and non-movement symptoms in Parkinson’s. A 2022 meta-analysis that separated the drugs by type found a difference in favor of CBD when it pooled three small studies with pure CBD published up to October 2021; however, these three studies had measured different things (movement and quality-of-life scores, anxiety triggered in the laboratory, a sleep disorder), and the main result of two of them was no different from placebo. The Brazilian Academy of Neurology wrote that there are no scientific data supporting the use of cannabinoids in Parkinson’s; the academy’s 2025 Parkinson’s guideline also found the evidence for cannabis in pain insufficient and stated that CBD does not reduce REM sleep behavior disorder. There is no Cochrane review on this topic.
Strength of evidence: ●●○○ Weak evidence. Finding: No effect found. What does this mean?
Ongoing research on this topic
Trials testing CBD for this topic on ClinicalTrials.gov: 1 under way (1 recruiting); results are awaited from 1 that ended in the last two years. A trial being under way does not show that CBD works.
- NCT06629389: Phase 2, recruiting, target 88 participants
- NCT07651930: Phase 2, completed, results awaited, 27 participants
Possible side effects and drug interactions
In studies with products containing CBD and a small amount of THC, mild side effects were more common in the treatment group; no serious side effects were reported. In one study, a blood value (alkaline phosphatase) rose in the CBD group. In a 13-person study that tried high-dose pure CBD (20–25 mg per kilogram of body weight a day), diarrhea and sleepiness were very common, liver enzymes rose in 5 people and 3 people had to stop the drug. With products containing more THC, side effects such as sleepiness, dizziness and confusion were reported more often. In healthy volunteers, CBD increased the risk of diarrhea; with THC-containing products, side effects involving the nervous system and mental health are more common.
People with Parkinson’s often take several medicines together. CBD can slow the breakdown of some medicines in the body; so drug interactions, liver values and the risk of sleepiness or falls matter.
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 |
|---|---|---|---|
| Quetiapine (Seroquel, Ketilept, Cedrina), Clozapine (Clonex, Leponex) | Information | Antipsychotics: No published study has measured antipsychotic blood levels with CBD. In schizophrenia studies, CBD (600–1000 mg a day) added for 6 weeks to the antipsychotic being taken was generally well tolerated; in one study, drowsiness was more common in those taking CBD. Drowsiness may increase when they are taken together; tell your doctor. | PMID 29241357, PMID 29619533, FDA Epidiolex label §7.4 (05/2026) |
| Clozapine (Clonex, Leponex) | Information | Clozapine: No study has looked at clozapine and CBD together. Clozapine is broken down mainly by CYP1A2, and also by CYP2D6 and CYP3A4; approved CBD raised the total amount in the blood of caffeine, which is broken down by CYP1A2, about 2-fold. The clozapine prescribing information recommends close monitoring of the patient, and lowering the clozapine dose if needed, when it is combined with weak or moderate CYP1A2 inhibitors such as caffeine and birth control pills. Do not start without talking to your psychiatrist. | PMID 33951339, FDA Epidiolex label §7.2 (05/2026), Clozapine prescribing information §2.7 and §7.1, dailymed.nlm.nih.gov |
To check interactions with the medicines you take: CBD drug interaction checker.
How was CBD used in studies?
Pure CBD studies used 75–300 mg a day (study dose; not a personal recommendation) and a single dose of 300 mg (study dose; not a personal recommendation). In an uncontrolled safety study, the dose was raised up to 20–25 mg per kilogram of body weight a day (study dose; not a personal recommendation); at this dose, liver values rose. With products containing CBD and a small amount of THC, the daily dose was between about 15.6–191.8 mg of CBD and 0.6–6.4 mg of THC (study dose; not a personal recommendation). In these studies, the dose was adjusted gradually over 1–2 weeks according to the research plan. In the nabilone studies, the daily dose was started at 0.25 mg and adjusted up to at most 2 mg (study dose; not a personal recommendation).
Study details (for health professionals)
All RCTs with CBD-containing products for motor symptoms, levodopa-related involuntary movements, pain and REM sleep behavior disorder were negative; on some measures (sleep, cognition, quality of life), placebo did better. In most of these RCTs, the CBD came with a small amount of THC. For psychosis there is only one 6-patient open-label study; no RCT was found. The tremor and anxiety data come from a single-dose laboratory test; they do not count as evidence for daily use. Two small RCTs with a THC-like synthetic drug (nabilone), however, reported positive results: a 7-person crossover study on levodopa-related involuntary movements and a 38-person study on non-movement symptoms in which drug responders were selected first (enriched design); both are small and their designs may inflate the effect. In the 6-month open extension study with responders, the improvement in sleep and pain continued; the improvement in the total non-movement symptom score, however, was borderline, and there was no control group. Studies without a comparison group (high-dose pure CBD, smoked marijuana, medical marijuana at doses patients adjusted themselves, a chart review of patients given medical marijuana in routine practice) reported improvement; these designs cannot separate out the effect of expectation, and liver enzymes rose with high-dose CBD. In a 1–3-year matched comparison of medical marijuana users, no worsening was seen in disease progression or mental health symptoms (observational). The most recent meta-analysis pooling the RCTs (Messak 2026) found no significant benefit for movement and non-movement symptoms; a meta-analysis that separated the drugs by type (Bilbao 2022) found a difference in favor of CBD when it pooled three small studies with pure CBD, but these studies had measured different outcomes, and studies published after October 2021 were not included in this analysis. The Brazilian Academy of Neurology wrote that there are no scientific data supporting the use of cannabinoids in Parkinson’s; the academy’s 2025 Parkinson’s guideline also found the evidence for cannabis in pain insufficient. Cannabinoids are not included in the UK’s NICE Parkinson’s guideline or in the International Parkinson and Movement Disorder Society’s evidence-based treatment reviews for non-motor symptoms (2019) and motor fluctuations (2025). October 2026 search (PubMed, Cochrane, ClinicalTrials.gov): on this topic we found 10 randomized, placebo-controlled studies with cannabinoids (the largest 101 people), 6 studies without a comparison group, 1 observational comparison, 3 systematic reviews and a position paper from a national academy of neurology; there is no Cochrane review. All are in the table below. An 8-person dose-finding study that did not measure efficacy and a guideline that was later withdrawn were not included in the table.
Evidence assessment: Weak
CBD alone
In three small controlled studies with pure CBD, there was no clear difference from placebo in movement symptoms (21 people, 6 weeks) or REM sleep behavior disorder (33 people, 14 weeks); a single 300 mg dose reduced anxiety and tremor triggered in the laboratory. A 2022 meta-analysis pooling these three studies found a difference in favor of CBD; however, the studies had measured different things, and in two of them the movement or sleep measures were no different from placebo. In a 13-person uncontrolled study with a very high dose (20–25 mg per kilogram of body weight a day), improvement in movement scores was reported; the tremor score, however, did not change clearly (this result is only on the study’s registry page and was not tested statistically), and liver enzymes rose in 5 people. For psychosis there is only one 6-patient open-label study. The strength of evidence is weak.
Products containing THC
RCTs with products containing CBD + low THC showed no benefit for motor symptoms, pain or cognition; some results favored placebo. Cannabis extract capsules containing THC and CBD did not reduce levodopa-related involuntary movements (19-person crossover RCT); with short-term CBD + low THC, a slight worsening was seen on a verbal fluency test. Two small RCTs with the THC-like synthetic drug nabilone reported positive results (levodopa-related involuntary movements, 7 people; non-movement symptoms, 38 people in a study in which only drug responders were randomized); in the 6-month open extension study of responders, the improvement in sleep and pain continued (no control group). Three uncontrolled studies with smoked marijuana (22 people) and medical marijuana (a 50-person prospective and a 69-person retrospective study) reported improvement in movement or non-movement symptoms; because there was no comparison group, the effect of expectation cannot be separated out. In a 1–3-year matched comparison of 76 patients using medical marijuana, no relative worsening was seen in disease progression or in psychosis, depression and cognition (observational). The strength of evidence is weak.
Evidence: Weak (RCTs with products containing THC and CBD negative; two small RCTs with nabilone positive)
Dose range in studies
Pure CBD 75–300 mg/day and a single 300 mg dose; in an uncontrolled safety study, pure CBD up to 20–25 mg/kg/day; CBD + low THC products ~15.6–191.8 mg CBD + 0.6–6.4 mg THC/day; nabilone 0.25–2 mg/day
Starting dose and titration
In the studies, treatment started at a low dose and was raised to the target dose over 1–2 weeks (Liu 2024: 2.5 mg/kg/day over 2 weeks; Kanjanarangsichai 2022: 2 weeks of individual titration); these are research protocols
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 |
|---|---|---|---|---|---|---|
| Liu 2024 Double-blind, placebo-controlled RCT | 61 (31/30) Parkinson’s | Cannabis extract, oral solution in sesame oil (100 mg/mL CBD + 3.3 mg/mL THC; contains THC) | Avg. 191.8 mg CBD + 6.4 mg THC/day (2.5 mg/kg/day) 2 weeks of titration | ~2 weeks (at the final dose) | No difference from placebo on motor MDS-UPDRS (difference −1.80 points; 95% CI −5.88 to 2.27; p = 0.379; marked improvement in the placebo group too); sleep and cognition results favored placebo Side effects: Mild side effects more common in the CBD/THC group | PMID 38487964, doi:10.1002/mds.29768, NCT03582137, July 23, 2024), PMID 37212386, 29 vs. 29 people, after adjusting for age and education, the CBD/THC group did worse than placebo on the animal naming test, and cognitive side effects were at least twice as common), PMID 38466972, on the Skin Conditions topic) |
| Kubota 2026 Phase 2, placebo-controlled RCT | 101 (87 completed) Painful Parkinson’s disease | CBD 96 mg/mL + THC 2.1 mg/mL | Final dose 43.88 mg CBD + 0.96 mg THC/day not reported | 9 weeks | No difference from placebo on the primary outcome (Parkinson’s pain classification system score) (p = 0.757); no difference on other non-motor symptom scales either Side effects: No serious side effects | PMID 42563548, doi:10.1002/mds.70449 |
| Mitarnun 2025 Double-blind RCT | 60 (51 analyzed) Parkinson’s | Sublingual CBD-rich product (101.9 mg/mL CBD + 4.8 mg/mL THC; contains THC) | Avg. 26 mg CBD + 1.2 mg THC/day not reported | 12 weeks | No difference on the primary outcome (delayed recall); small increase in naming score Side effects: Alkaline phosphatase rose in the CBD group; no serious side effects | PMID 40267585, doi:10.1016/j.parkreldis.2025.107841 |
| Kanjanarangsichai 2022 Double-blind RCT | 40 (36 analyzed) Parkinson’s | Sublingual CBD-rich cannabis flower extract in olive oil (100 mg/mL CBD + 3.9 mg/mL THC; contains THC) | Avg. 15.59 mg CBD + 0.61 mg THC/day 2 weeks of individual titration | 8 weeks | No difference in UPDRS, gait, anxiety or depression; quality of life better with placebo Side effects: Side effect frequency similar in the two groups (47.3% vs. 47.1%), all mild (most common: dry throat); no serious side effects | PMID 36743777, doi:10.25259/JNRP-2022-6-19 |
| Chagas 2014 Exploratory double-blind study | 21 (3 × 7) Parkinson’s | Pure CBD (99.9% pure powder in corn oil, capsule; according to reviews); added to Parkinson’s medicines | 75 or 300 mg/day not reported | 6 weeks (according to review tables) | No difference on the UPDRS; in the 300 mg group, quality of life (PDQ-39) differed from placebo (p=0.05) Side effects: No notable side effects in any group on the side effect scale (UKU) or in verbal reports (according to a review table; full text could not be read) | PMID 25237116, doi:10.1177/0269881114550355, Duration and product from review tables (PMC6710502, PMC8161868), full text not read |
| de Faria 2020 Double-blind, placebo-controlled, crossover RCT (2 sessions, 15 days apart; simulated public speaking test) | 24 (22 men, 2 women; sex distribution according to a review table) Parkinson’s patients (Brazil; mean age 64, mean disease duration 6.5 years, Hoehn-Yahr stage 1–2.5; 19 of 24 were taking levodopa; according to a review table) | Oral CBD capsule (powder, 99.9% pure, in corn oil; product information according to a review table, full text could not be read); placebo identical capsule | 300 mg single dose None | Single session | Drug effect favoring CBD on the anxiety dimension of the Visual Analog Mood Scale: the anxiety caused by the speaking test decreased. Tremor amplitude measured with an accelerometer decreased with CBD (p = 0.022); no difference in tremor frequency or in the other tremor measure (p = 0.899 and 0.216), and no difference on the finger-tapping test (slowness of movement) either (p = 0.701; tremor and finger-tapping results according to a review table). Limited to a single dose and two laboratory sessions. Public funding (São Paulo Research Foundation FAPESP and Brazil’s National Council for Scientific and Technological Development CNPq; according to a review table); conflict of interest statement could not be read; of the 9 authors, Zuardi, Hallak and Crippa report in their other publications (e.g., Linares 2019, Bolsoni 2022b) that they are inventors on a CBD derivative patent and that their university has an agreement with a pharmaceutical company to develop a synthetic CBD product, including for Parkinson’s disease Side effects: No side effects reported during or after the sessions (according to a review table; full text could not be read). Pulse and blood pressure were measured during the speaking test; the results are not in the abstract or the review table | PMID 31909680, doi:10.1177/0269881119895536, Secondary source for product, participant characteristics, funding, PMID 34104218, PMC8161868, Tables 1, 2, 5 and 6) |
| Sieradzan 2001 Double-blind, placebo-controlled, randomized crossover pilot study | 7 Parkinson’s patients with levodopa-related involuntary movements (dyskinesia) | Nabilone (THC-like synthetic cannabinoid, by mouth) | 0.03 mg/kg nabilone, divided into two doses 12 hours and 1 hour before the levodopa test (according to a review table) None (single day, divided into two doses) | A single treatment day (divided into two doses); two levodopa tests 2 weeks apart (according to a review table) | Nabilone significantly reduced levodopa-related dyskinesia compared with placebo (very small study) Side effects: With nabilone, 2 patients were withdrawn from the study (one for dizziness, one for a symptomatic drop in blood pressure on standing); in 5 patients, mild sleepiness, a floating sensation, dizziness, oversensitivity to sounds, partial disorientation or visual hallucinations (according to a review table; full text could not be read) | PMID 11739835, doi:10.1212/wnl.57.11.2108 |
| Peball 2020 Phase 2, double-blind, placebo-controlled, enriched randomized withdrawal design (open-label dose finding first, then responders randomized) | 47 in the open-label period; 38 randomized (19/19) Parkinson’s patients with stable motor symptoms and troublesome non-motor symptoms (Austria) | Nabilone (THC-like synthetic cannabinoid, oral capsule) | Started at 0.25 mg a day, up to at most 1 mg twice a day; median 0.75 mg/day in the randomized period In the open-label period, 0.25 mg/day → at most 2 × 1 mg | Open-label dose finding + 4-week randomized period | MDS-UPDRS-I (non-motor symptoms) worsened by 2.63 points with placebo and 1.00 point with nabilone over 4 weeks (difference 1.63; p = 0.030). Because only drug responders were randomized, the effect may look larger than it would be across all patients. The manufacturer supplied the drug and placebo and covered the costs of visits and independent monitoring; 5 of the 18 authors have ties to the manufacturer (one is a company employee) Side effects: Side effects in 77% in the open-label period (mostly temporary); in the double-blind period 32% (nabilone) and 42% (placebo); no serious side effects | PMID 32757413, doi:10.1002/ana.25864, NCT03769896, March 2, 2021), EudraCT 2017-000192-86, PMID 31129719, PMID 35937495, sleep problems worsened only in those who switched to placebo), PMID 35625047, no difference from placebo). The open-label extension study is in a separate row (Peball 2024) |
| Carroll 2004 Double-blind, placebo-controlled, randomized crossover RCT (preceded by a 6-patient open dose-escalation study) | 19 randomized; 17 completed (plus a 6-person dose-finding pilot study) Parkinson’s patients with levodopa-related involuntary movements (dyskinesia) (England) | Cannador: ethanol extract of the cannabis plant, oral capsule (contains THC and CBD; according to a review table, more THC than CBD) | By body weight; mean 0.146 mg/kg/day (according to a review table; full text could not be read) Dose escalation was tried in the pilot study; the adjustment schedule in the RCT is not in the abstract | 2 × 4 weeks (2-week washout in between) | No difference from placebo on the primary outcome (UPDRS items 32–34: dyskinesia); no difference on secondary measures either (Rush and Bain dyskinesia scales, total UPDRS after a levodopa test, quality of life PDQ-39, on-off diaries). The cannabis extract neither improved nor worsened Parkinson’s symptoms. By the review’s calculation, the difference in UPDRS dyskinesia score was 0.52 (95% CI −0.1 to 1.1; p = 0.09), in the direction against cannabis but not significant Side effects: Physical side effects 18 with cannabis, 9 with placebo; mental side effects (sleepiness, feeling detached, suspiciousness, nightmares, confusion, forgetfulness) 20 with cannabis, 6 with placebo (given as “n” in the review table; not stated whether people or events); all mild and resolved when the dose was reduced; no serious side effects | PMID 15477546, doi:10.1212/01.wnl.0000140288.48796.8e, Commentary and author reply: Neurology 2005, PMID 15781848, content not read) |
| de Almeida 2021 (RBD) Phase 2/3, double-blind, placebo-controlled RCT (parallel, 1:1) | 33 randomized Parkinson’s patients with REM sleep behavior disorder (a sleep disorder in which dreams are acted out with movements) (Brazil) | Pure CBD capsule (added to Parkinson’s medicines) | 75–300 mg/day From 75 mg to 300 mg (schedule not in the abstract) | 14 weeks | No difference from placebo on the primary outcomes (frequency of nights with REM sleep behavior disorder, the physician’s global impression scales CGI-I and CGI-S). On secondary outcomes, a temporary improvement in sleep satisfaction with 300 mg between weeks 4 and 8 (p = 0.049 and p = 0.038). According to the authors, CBD as an add-on treatment did not reduce the symptoms of this disorder Side effects: Not reported (in the abstract; full text could not be read) | PMID 33754375, doi:10.1002/mds.28577, PMID 35749710, 18 patients, 6 CBD / 12 placebo, no difference on primary and secondary outcomes). Both are also in the table for the Insomnia topic |
| Messak 2026 Systematic review and meta-analysis of RCTs (PubMed, Scopus, Web of Science; risk of bias RoB-2) | 11 RCTs; 6 in the meta-analysis Parkinson’s patients | Cannabinoids (CBD, CBD with THC, nabilone, etc.) | Variable | Cannabinoids did not change disease severity (SMD 0.16; 95% CI −0.13 to 0.44), motor examination (SMD −0.08; −0.35 to 0.20), motor difficulties in daily life (SMD −0.08; −0.49 to 0.33) or non-motor symptoms (SMD −0.03; −0.72 to 0.67; high heterogeneity between studies) significantly differently from placebo. When the nabilone study was removed, the estimate for non-motor symptoms changed (SMD 0.34; −0.19 to 0.88); according to the authors, the signal of benefit seen with nabilone is a separate question and needs its own trial. The authors note as a limitation that earlier reviews also pooled drugs that block the cannabinoid receptor Side effects: Not reported in the abstract | PMID 42138778, doi:10.1007/s13760-026-03082-0 | |
| Bilbao 2022 Systematic review and meta-analysis of RCTs separated by drug type (up to October 2021; GRADE) | 152 RCTs (all indications, 12,123 participants); in Parkinson’s, 3 RCTs with pure CBD (101 participants) and 2 RCTs with nabilone (51 participants) All medical indications (including a Parkinson’s subgroup) | Dronabinol, nabilone, pure CBD and nabiximols (natural products such as smoked cannabis excluded) | Variable (75–300 mg/day or a single dose in the Parkinson’s CBD studies) | In Parkinson’s, all cannabinoids together were found better than placebo (SMD −0.41; 95% CI −0.69 to −0.13). In the subgroup, the three small pure CBD studies (Chagas 2014, de Faria 2020, de Almeida 2021) were significant (SMD −0.41; −0.75 to −0.08; GRADE: moderate), while the two nabilone studies were not (SMD −0.38; −1.05 to 0.29; very low). However, these three CBD studies had measured different things (movement and quality-of-life scores, anxiety triggered in the laboratory, REM sleep behavior disorder), and in two of them the movement or sleep measures were no different from placebo; which measures were pooled is shown only in a figure. Later RCTs (2022–2026) were not included in this analysis Side effects: Across all indications, the likelihood of any side effect with CBD higher than with placebo (OR 1.82; 95% CI 1.08–3.07); no Parkinson’s-specific side effect analysis | PMID 35982439, doi:10.1186/s12916-022-02459-1, PROSPERO CRD42021229932 | |
| Urbi 2022 Systematic review and meta-analysis (up to June 2021) | 5 RCTs and 18 non-randomized studies Parkinson’s patients | Cannabis and cannabinoids (CBD, THC-containing products, nabilone) | Variable | No strong evidence was found that would be enough to recommend cannabis use in Parkinson’s. A possible signal of benefit was reported for tremor, anxiety, pain, sleep quality and quality of life; the authors stressed the scarcity of well-designed randomized studies. Meta-analysis numbers not in the abstract Side effects: Not reported in the abstract | PMID 34958046, doi:10.3233/JPD-212923 | |
| Brucki 2021 Position paper of a national academy of neurology (scientific departments of the Brazilian Academy of Neurology; literature assessment) | Not applicable Neurological diseases (including the movement disorders and sleep disorders sections) | Cannabinoids (CBD, THC, nabiximols, etc.) | Not applicable | According to the movement disorders section, there are no scientific data supporting the use of cannabinoids in Parkinson’s: the positive response in movement symptoms seen in uncontrolled studies was not repeated in controlled studies; reports of improvement in psychosis, sleep and pain mostly come from small, short and uncontrolled studies. The same academy’s 2025 Parkinson’s guideline (a separate document, other source) found the evidence for cannabis in pain insufficient (level U; at that time the only study in pain was an 8-person dose-finding study that did not measure efficacy) and wrote that CBD does not reduce REM sleep behavior disorder Side effects: Not applicable | PMID 34133518, doi:10.1590/0004-282X-ANP-2020-0432, Movement Disorders Department of the Brazilian Academy of Neurology, PMID 39993447, PMID 41173036, PMID 35319667 | |
| Leehey 2020 Open-label dose-escalation study; no control group | 15 enrolled, 13 started, 10 completed Parkinson’s patients with marked resting tremor who did not use cannabis (US) | Pure CBD oral solution (Epidiolex, 100 mg/mL) | From 5 mg/kg/day to 20–25 mg/kg/day Increased by 2.5–5 mg/kg every 3–5 days (per the registry) | Dose escalation + 10–15 days at a fixed dose (5 weeks in total per the registry) | In the 10 completers, total MDS-UPDRS fell by 7.7 points (17.8%; p = 0.012) and the motor section by 6.1 points (24.7%; p = 0.004); night-time sleep and emotional-behavioral control scores improved. No placebo. The patients selected for the study had marked tremor, but the change in tremor score was −0.4 points (SD 1.26; only in the registry results, no statistical test). The authors stressed that the high dose caused problems with liver values and that a randomized study is needed Side effects: Side effects in everyone: diarrhea 85%, sleepiness 69%, fatigue 62%, weight gain 31%, dizziness and abdominal pain 23%; at 20–25 mg/kg/day, liver enzymes rose in 5 people (38.5%) (mostly cholestatic (bile duct) type, 1 with symptoms); 3 people (23%) could not tolerate it and stopped; no serious side effects | PMID 33381646, doi:10.1089/can.2019.0068, NCT02818777, February 19, 2019, the registry title says crossover RCT, but only the open-label first phase was done). The manufacturer (GW Research Ltd) is listed as a collaborator in the registry, the publication’s abstract states there was no conflict of interest |
| Zuardi 2009 Open-label pilot, no control group | 6 Parkinson’s psychosis | Pure CBD | Started at 150 mg/day, flexible dose Flexible | 4 weeks | Psychotic symptoms decreased (no control). The conflict of interest statement and funding could not be read from the primary source (full text not open access); according to the table of a systematic review, the study was supported by Brazil’s national and state science funds, and the companies THC-Pharm (Germany) and STI-Pharm are also listed as supporters in the table (Thanabalasingam 2021). 3 of the 8 authors later became inventors on CBD patents (fluorinated CBD compounds; international application WO/2014/108899) Side effects: No side effects observed | PMID 18801821, doi:10.1177/0269881108096519, PMID 34104218, PMC8161868, Table 2) |
| Peball 2024 (NMS-Nab2) Open-label extension study (those who responded to nabilone in the NMS-Nab trial and completed the double-blind period without problems); no control group | 22 started; 21 analyzed; 19 completed Parkinson’s patients with non-motor symptoms who had previously responded to nabilone (Austria) | Nabilone (THC-like synthetic cannabinoid, oral capsule) | Mean 0.87 mg/day (range 0.25–1.5 mg) Re-titrated until non-motor symptoms improved | 6 months | According to the physician’s global impression, improvement was maintained in 79% of patients at the last visit. Compared with the state before restarting nabilone, overall sleep (NMSS domain 2 −8.26 points; 95% CI −13.82 to −2.71; p = 0.004), night-time sleep problems (MDS-UPDRS 1.7 −1.42; p = 0.002) and pain (KPPS −8.00; 95% CI −15.05 to −0.95; p = 0.046) were better; the drop in the total non-motor symptom score, however, was borderline (MDS-UPDRS-I −2.58; p = 0.052), and the scales (except the depression subscale) did not change significantly over the 6-month follow-up. No control group and only prior responders were enrolled; the results cannot be generalized to all patients. The drug was supplied by the manufacturer; 2 of the 12 authors reported fees from the manufacturer outside the study Side effects: Most common: difficulty concentrating; 1 person stopped because of a side effect (night-time sleep problem); in the registry, 4 serious events in 22 people (rectal cancer, lumbar disc herniation, worsening of Parkinson’s symptoms, vomiting; relationship to the drug not stated in the registry) | PMID 38491070, doi:10.1038/s41531-024-00665-7, NCT03773796, March 2, 2021), the main trial is Peball 2020 in the table |
| Lotan 2014 Open-label observational study (before-after); no placebo or control group | 22 Parkinson’s patients using medical marijuana (Israel, 2011–2012) | Smoked marijuana (contains THC; patients’ own product) | 0.5 g (according to a review table) None | Single session (before smoking and 30 minutes after) | UPDRS motor score fell from 33.1 to 23.2 (p < 0.001); improvement in tremor, muscle stiffness and slowness of movement, as well as in sleep and pain scores, was reported. No placebo, open assessment, and patients were already using marijuana; the effect of expectation cannot be separated out. Controlled studies with products taken by mouth did not show improvement in movement symptoms; there is no controlled study with smoked marijuana Side effects: No notable side effects observed (abstract); according to a review table, low blood sugar in 1 person and dizziness in 1 person | PMID 24614667, doi:10.1097/WNF.0000000000000016 |
| Anis 2026 Single-center, open-label prospective cohort; no control group | 68 started; 50 completed follow-up (26.5% dropout, mostly lost to follow-up) Parkinson’s patients newly starting medical marijuana (Israel) | Cannabis oil extract or dried flower; variable THC/CBD ratio (product content measured in the laboratory) | Dose adjusted by the patient (details not in the abstract) Self-titration | 3 months | At 3 months vs. baseline, total non-motor symptoms (NMSS) improved by 14.5 points (p = 0.001), sleep (PDSS-2) by 5.9 points (p < 0.001), pain (KPPS) by 8.1 points (p = 0.004) and quality of life (PDQ-8) by 1.5 points (p = 0.040); night-time urination frequency decreased (median 0.5; p = 0.016), while daytime urination measures did not change. No link was found between the product’s THC/CBD composition and response. No control group and no blinding Side effects: Generally well tolerated (abstract); side effect details not in the abstract | PMID 42304702, doi:10.1177/25785125261458680, NCT05106504, same scales and product analysis, status “unknown” in the registry, no results entered), the publication’s abstract gives no registration number |
| Goldberg 2023 Retrospective case-control study (matched comparison) | 152 (76 medical marijuana users, 76 matched controls) Patients with idiopathic Parkinson’s disease (Israel, single center, 2008–2022) | Whole-plant medical marijuana (median 10% THC, 4% CBD) | Median 20 g/month | At least 1 year of use; 1–3 years of follow-up | Levodopa equivalent dose and disease stage (Hoehn and Yahr) progressed similarly in the two groups (p = 0.90 and p = 0.77); no relative worsening in the marijuana group in psychosis, depression and cognitive problems reported by patients to their physician (p = 0.16–0.50). Retrospective and not randomized; patients chose to use marijuana. Observational data Side effects: No safety concerns with long-term use in terms of disease progression and mental health symptoms (abstract); other side effects not in the abstract | PMID 37211456, doi:10.1016/j.parkreldis.2023.105406 |
| Aladeen 2023 Retrospective chart review (single center); no control group | 69 Parkinson’s patients given medical marijuana in routine practice (US, New York State, single neurology center) | Medical marijuana products; most patients started on a tincture with equal amounts of THC and CBD (1:1), followed by changes in ratio and form | not reported (in the abstract) Ratio and form adjusted in routine practice (details not in the abstract) | not reported (in the abstract) | According to the records, improvement in at least one symptom was noted in 60 of 69 patients (87%); most often in muscle cramps and dystonia, pain, muscle stiffness, loss of appetite, involuntary movements and tremor. 56% of opioid users (14 people) reduced or stopped their opioid (mean daily morphine equivalent from 31 to 22 mg). Retrospective with no comparison group; improvement was determined from physician notes rather than standard scales, and the effects of expectation and patient selection cannot be separated out. 1 of the 8 authors has a financial interest in a cannabis company (according to the authors, patients did not use this company’s products); funding from a nonprofit foundation Side effects: No serious side effects reported; 4 patients stopped because of side effects | PMID 37191563, doi:10.1097/WNF.0000000000000550 |
Reported side effects
- In healthy volunteers, CBD increased the risk of diarrhea (RR 5.85); non-significant trend toward more abdominal pain and headache (Sawaira 2026, PMID 41789242)
- Psychiatric and nervous system side effects more common with THC-containing products (Filippini 2022, PMID 35510826); the likelihood of side effects increased with any cannabinoid (OR 1.75; Wilson 2026, PMID 41856154)
- Raised alkaline phosphatase (Mitarnun 2025)
- Mild side effects more common in the CBD/THC group (Liu 2024)
- With high-dose pure CBD (20–25 mg/kg/day), raised liver enzymes in 5 of 13 patients; diarrhea 85%, sleepiness 69%, stopping because of side effects 23% (Leehey 2020)
- With a cannabis extract containing THC and CBD, mental side effects (sleepiness, confusion, suspiciousness, nightmares) more common than with placebo (Carroll 2004); with nabilone, dizziness, a drop in blood pressure on standing and visual hallucinations were reported (Sieradzan 2001). The full text of both studies could not be read; the information comes from the tables of a systematic review
Monitoring done in studies
- People with Parkinson’s take many medicines: drug interactions, liver enzymes and falls/sedation should be monitored with the doctor
Who should be careful
- High doses cannot be compared with market doses: in low-dose (≤175 mg/day) studies, plasma levels were 5–100 times lower than with the 20 mg/kg Epidiolex dose (Warren 2026, PMID 42473010)
- Anyone taking long-term medicines should talk to a doctor before starting; the studies on this page did not systematically assess interactions
Drug interactions
- The studies on this page did not systematically assess drug interactions; details are in the site’s Drug interactions section
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 stop or change your Parkinson’s medicines on your own; there is no evidence that CBD can replace them.
- Review all the medicines you take with your neurologist and pharmacist; checking for drug interactions is important.
- If you decide to use CBD, ask your doctor to monitor your liver values and your risk of sleepiness and falls.
- Check the product label and certificate of analysis (COA); most of the products in the studies also contained a small amount of THC.
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
Well-designed studies of CBD in Parkinson’s did not show a benefit for movement symptoms, pain or sleep problems; signals for anxiety, tremor and psychosis rest on very small or one-time studies. Talking with your neurologist before trying anything new is the safest path.
Frequently asked questions
Does CBD oil work for Parkinson’s?
Current studies do not support this. In studies in which patients were split into groups by chance, CBD-rich products did not do better than an inactive pill (placebo) for movement symptoms, pain or thinking skills. On some measures, the placebo group did better. A cannabis extract containing THC and CBD also did not help with involuntary movements caused by the medicine levodopa. Most of these studies were small and short; the strength of evidence is weak.
Does CBD reduce tremor in Parkinson’s?
In a laboratory study with 24 patients, a single dose of CBD reduced the severity of stress-triggered tremor. But this was a one-time test. In an uncontrolled study in which high-dose pure CBD was tried for a few weeks in 13 patients with marked tremor, the tremor score did not change clearly (this result appears only on the study’s registry page and was not tested statistically). In a 22-person uncontrolled study with smoked marijuana, a reduction in tremor was reported 30 minutes later, but there was no comparison group. There is no controlled study showing that it reduces tremor with daily use; the strength of evidence is weak.
Does CBD help with psychosis symptoms in Parkinson’s?
On this question there is only one 6-patient study without a comparison group. A reduction in symptoms was reported, but because no well-designed study has been done, nothing definite can be said.
Can CBD be used together with Parkinson’s medicines?
Parkinson’s studies did not look at drug interactions specifically. Because people with Parkinson’s often take several medicines, if you are considering CBD it is important to assess interactions with your neurologist and pharmacist.
Can CBD oil for Parkinson’s 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 classed as medicines and health products 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 (licensed) CBD medicine in Turkey. If you are thinking of using it, talk to your doctor first.
Does CBD help with sleep problems in Parkinson’s?
In REM sleep behavior disorder, which often comes with Parkinson’s and in which dreams are acted out with movements such as shouting or kicking, 14 weeks of pure CBD in a 33-patient study did not reduce these episodes differently from an inactive pill (placebo); only a temporary increase in sleep satisfaction lasting a few weeks was seen. In a 61-person study with a product containing CBD and a small amount of THC, sleep measures favored placebo. In a later (not pre-planned) analysis of a small study with the THC-like synthetic drug nabilone, sleep problems got worse in those who stopped the drug and switched to placebo; however, only patients who responded to the drug had been enrolled in this study. The strength of evidence is weak.
References
Show 21 references
- Liu 2024. Double-blind, placebo-controlled RCT. PMID 38487964, doi:10.1002/mds.29768, NCT03582137, July 23, 2024), PMID 37212386, 29 vs. 29 people, after adjusting for age and education, the CBD/THC group did worse than placebo on the animal naming test, and cognitive side effects were at least twice as common), PMID 38466972, on the Skin Conditions topic)
- Kubota 2026. Phase 2, placebo-controlled RCT. PMID 42563548, doi:10.1002/mds.70449
- Mitarnun 2025. Double-blind RCT. PMID 40267585, doi:10.1016/j.parkreldis.2025.107841
- Kanjanarangsichai 2022. Double-blind RCT. PMID 36743777, doi:10.25259/JNRP-2022-6-19
- Chagas 2014. Exploratory double-blind study. PMID 25237116, doi:10.1177/0269881114550355, Duration and product from review tables (PMC6710502, PMC8161868), full text not read
- de Faria 2020. Double-blind, placebo-controlled, crossover RCT (2 sessions, 15 days apart; simulated public speaking test). PMID 31909680, doi:10.1177/0269881119895536, Secondary source for product, participant characteristics, funding, PMID 34104218, PMC8161868, Tables 1, 2, 5 and 6)
- Sieradzan 2001. Double-blind, placebo-controlled, randomized crossover pilot study. PMID 11739835, doi:10.1212/wnl.57.11.2108
- Peball 2020. Phase 2, double-blind, placebo-controlled, enriched randomized withdrawal design (open-label dose finding first, then responders randomized). PMID 32757413, doi:10.1002/ana.25864, NCT03769896, March 2, 2021), EudraCT 2017-000192-86, PMID 31129719, PMID 35937495, sleep problems worsened only in those who switched to placebo), PMID 35625047, no difference from placebo). The open-label extension study is in a separate row (Peball 2024)
- Carroll 2004. Double-blind, placebo-controlled, randomized crossover RCT (preceded by a 6-patient open dose-escalation study). PMID 15477546, doi:10.1212/01.wnl.0000140288.48796.8e, Commentary and author reply: Neurology 2005, PMID 15781848, content not read)
- de Almeida 2021 (RBD). Phase 2/3, double-blind, placebo-controlled RCT (parallel, 1:1). PMID 33754375, doi:10.1002/mds.28577, PMID 35749710, 18 patients, 6 CBD / 12 placebo, no difference on primary and secondary outcomes). Both are also in the table for the Insomnia topic
- Messak 2026. Systematic review and meta-analysis of RCTs (PubMed, Scopus, Web of Science; risk of bias RoB-2). PMID 42138778, doi:10.1007/s13760-026-03082-0
- Bilbao 2022. Systematic review and meta-analysis of RCTs separated by drug type (up to October 2021; GRADE). PMID 35982439, doi:10.1186/s12916-022-02459-1, PROSPERO CRD42021229932
- Urbi 2022. Systematic review and meta-analysis (up to June 2021). PMID 34958046, doi:10.3233/JPD-212923
- Brucki 2021. Position paper of a national academy of neurology (scientific departments of the Brazilian Academy of Neurology; literature assessment). PMID 34133518, doi:10.1590/0004-282X-ANP-2020-0432, Movement Disorders Department of the Brazilian Academy of Neurology, PMID 39993447, PMID 41173036, PMID 35319667
- Leehey 2020. Open-label dose-escalation study; no control group. PMID 33381646, doi:10.1089/can.2019.0068, NCT02818777, February 19, 2019, the registry title says crossover RCT, but only the open-label first phase was done). The manufacturer (GW Research Ltd) is listed as a collaborator in the registry, the publication’s abstract states there was no conflict of interest
- Zuardi 2009. Open-label pilot, no control group. PMID 18801821, doi:10.1177/0269881108096519, PMID 34104218, PMC8161868, Table 2)
- Peball 2024 (NMS-Nab2). Open-label extension study (those who responded to nabilone in the NMS-Nab trial and completed the double-blind period without problems); no control group. PMID 38491070, doi:10.1038/s41531-024-00665-7, NCT03773796, March 2, 2021), the main trial is Peball 2020 in the table
- Lotan 2014. Open-label observational study (before-after); no placebo or control group. PMID 24614667, doi:10.1097/WNF.0000000000000016
- Anis 2026. Single-center, open-label prospective cohort; no control group. PMID 42304702, doi:10.1177/25785125261458680, NCT05106504, same scales and product analysis, status “unknown” in the registry, no results entered), the publication’s abstract gives no registration number
- Goldberg 2023. Retrospective case-control study (matched comparison). PMID 37211456, doi:10.1016/j.parkreldis.2023.105406
- Aladeen 2023. Retrospective chart review (single center); no control group. PMID 37191563, doi:10.1097/WNF.0000000000000550
Points that could not be verified from the full text
- Full text of Chagas 2014 not read (paywalled); duration (6 weeks), product and side effect information (no notable side effects on the side effect scale) taken from review tables
- The full texts of Carroll 2004 and Sieradzan 2001 could not be accessed (the publisher page required bot verification); product content, dose and side effect information were taken from the tables of a systematic review. The amount of THC per capsule in Carroll 2004 could not be verified from the primary source.
- In the Bilbao 2022 meta-analysis, which measures were pooled from the three CBD studies is shown only in a figure and could not be verified from the text. For Messak 2026, Urbi 2022, Kubota 2026, Mitarnun 2025, de Almeida 2021, Leehey 2020, Lotan 2014, Anis 2026, Goldberg 2023 and Aladeen 2023, only the abstracts were read; the tremor result of Leehey 2020 is from the study’s ClinicalTrials.gov registry entry.
- A study with unpublished results: a 27-person double-blind study in Warsaw comparing the effect of three doses of full-spectrum CBD oil (30, 60 and 300 mg a day) on anxiety and depression in Parkinson’s patients finished in November 2024 (NCT07651930); as of October 2026, there are no results or publications in the registry. Because there is no placebo group, even if results come out they will answer the question of efficacy only in a limited way.
Research history
Here we record what changed on this page, when and why, with dates. The newest change is at the top.
The last sentence of the page's short summary was rewritten in a calmer, more guiding tone: instead of "Talk to your doctor before you start.", it now says whom you can talk with, and about what, if you are considering CBD. The conclusion and the strength of evidence did not change.
October 2026 supplementary review: sources found for this page during the searches for other topics were read and added to the page. The row for the study looking at the effect of a single dose of CBD on anxiety during a speaking test (de Faria 2020) was made consistent with the same study’s row on the Social Anxiety page: the placebo-controlled crossover design, the purity of the product (99.9% pure CBD powder), the participants’ sex and disease stage, public funding, and details of the tremor measurements (tremor amplitude went down; its frequency and slowness of movement did not change) were added from the tables of a systematic review; the results for the measured pulse and blood pressure could not be accessed. The same row now notes a CBD derivative patent that three of the authors reported in their other publications, and their university’s agreement with a pharmaceutical company to develop a synthetic CBD product, including for Parkinson’s disease. In the row for the small open-label study in Parkinson’s psychosis (Zuardi 2009), it is now stated clearly that the funding information could not be read from the primary source and came from a review table; it was added that the authors’ CBD patents date from the years after the study (consistent with the same row on the Schizophrenia page). The conclusion and the strength of evidence did not change.
Display fix: internal working notes left over from the earlier cleanup were removed; content and evidence did not change.
Older changes (6)
PubMed, Cochrane and ClinicalTrials.gov were systematically searched again in October 2026 (1,464 records in PubMed and 270 in ClinicalTrials.gov; together with an independent second check). Added: 2 placebo-controlled randomized studies (a cannabis extract containing THC and CBD for levodopa-related involuntary movements, and pure CBD for REM sleep behavior disorder; neither differed from placebo), 3 systematic reviews and meta-analyses, the position paper of the Brazilian Academy of Neurology (together with the same academy’s 2025 Parkinson’s guideline), 5 studies without a comparison group (high-dose pure CBD, the 6-month extension study of nabilone, smoked marijuana, medical marijuana at doses patients adjusted themselves, a chart review of patients given medical marijuana in routine practice) and an observational comparison of long-term medical marijuana use. There is no Cochrane review on this topic. A small dose-finding study that did not measure efficacy and a guideline that was later withdrawn were not included in the table. Corrected: the CBD and THC amounts of the products in the studies, the numbers for primary outcomes, missing side effect information, company ties in two studies, additional publications and registration numbers of the same trials, and the table order; the explanation of the THC strength of evidence was updated in light of the new study (level unchanged). The conclusion and the strength of evidence did not change.
Related studies: Carroll 2004, published October 12, 2004 (PMID 15477546, doi:10.1212/01.wnl.0000140288.48796.8e, Commentary and author reply: Neurology 2005, PMID 15781848, content not read)); de Almeida 2021 (RBD), published July 2021 (PMID 33754375, doi:10.1002/mds.28577, PMID 35749710, 18 patients, 6 CBD / 12 placebo, no difference on primary and secondary outcomes). Both are also in the table for the Insomnia topic); Messak 2026, published May 15, 2026 (PMID 42138778, doi:10.1007/s13760-026-03082-0); Bilbao 2022, published August 19, 2022 (PMID 35982439, doi:10.1186/s12916-022-02459-1, PROSPERO CRD42021229932); Urbi 2022, published 2022 (PMID 34958046, doi:10.3233/JPD-212923); Brucki 2021, published April 2021 (PMID 34133518, doi:10.1590/0004-282X-ANP-2020-0432, Movement Disorders Department of the Brazilian Academy of Neurology, PMID 39993447, PMID 41173036, PMID 35319667); Leehey 2020, published December 15, 2020 (PMID 33381646, doi:10.1089/can.2019.0068, NCT02818777, February 19, 2019, the registry title says crossover RCT, but only the open-label first phase was done). The manufacturer (GW Research Ltd) is listed as a collaborator in the registry, the publication’s abstract states there was no conflict of interest); Peball 2024 (NMS-Nab2), published March 15, 2024 (PMID 38491070, doi:10.1038/s41531-024-00665-7, NCT03773796, March 2, 2021), the main trial is Peball 2020 in the table); Lotan 2014, published 2014 (PMID 24614667, doi:10.1097/WNF.0000000000000016); Anis 2026, published June 16, 2026 (PMID 42304702, doi:10.1177/25785125261458680, NCT05106504, same scales and product analysis, status “unknown” in the registry, no results entered), the publication’s abstract gives no registration number); Goldberg 2023, published July 2023 (PMID 37211456, doi:10.1016/j.parkreldis.2023.105406); Aladeen 2023, published May–June 2023 (PMID 37191563, doi:10.1097/WNF.0000000000000550)
Display fix: internal working file names left in the text were removed; content and evidence did not change.
Two small controlled studies with the THC-like synthetic drug nabilone were added; the statement “all controlled studies are negative” was limited to CBD-containing products. For CBD, the conclusion and the strength of evidence did not change.
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.
The full texts of the studies were reread and the information on the page was checked against its sources. Corrected: duration, registration number and product information in the study table. Points that could not be verified from the full text went down from 2 items to 1 item. The conclusion and the strength of evidence did not change.
Page published. In this first assessment, 7 studies were reviewed.