Last updated 16 August 2026 · Originally published 22 December 2021
People with Parkinson’s understandably want every useful option, and CBD gets suggested a great deal.
The short version: the controlled trials have mostly been negative. Dose may be part of the explanation for motor symptoms, but it can’t explain every disappointing result. It also matters whether you mean CBD alone or cannabis containing THC.
CBD on its own
The early reports were encouraging and very small. A Brazilian team saw psychotic symptoms decline in six patients given CBD for four weeks,[1] and reported four patients whose REM sleep behaviour disorder — acting out dreams — improved.[2] Open-label, no controls, a handful of people.
The controlled trials that followed have been mostly disappointing.
A 2014 double-blind trial of 21 patients at 75 or 300 mg daily found no motor improvement, though the higher dose showed a possible quality-of-life gain.[3] A 2021 trial in 33 patients tested 75–300 mg specifically for REM sleep behaviour disorder — following up that four-patient case series — and found no reduction, though sleep satisfaction improved temporarily.[4]
One small controlled study was positive: a single 300 mg dose reduced anxiety and associated tremor during a simulated public speaking test.[5] That tested a stress response rather than everyday Parkinson’s symptoms, but it’s a genuine controlled result.
The dose problem
One thing worth noting before writing CBD off here.
An open-label study in 2020 took patients up to 20–25 mg per kilogram daily — for some, over 3,000 mg. Scores for motor function, nighttime sleep and emotional control improved during treatment. At two-week follow-up the total Parkinson’s score and nighttime sleep remained improved; the motor and emotional measures did not.[6] No blinding, no placebo, so it proves little.
Still, the contrast is stark. That study went up to 3,460 mg a day; the randomised trials of purified CBD used 75 to 300 mg.
It also found raised liver enzymes in five of 13 participants at the top of the range, resolving on stopping.
Cannabis containing THC
A 12-week randomised trial in 2025 gave 60 patients a CBD-dominant, low-THC sublingual product — averaging 26 mg CBD and 1.2 mg THC daily. Safe and well tolerated, but it missed its primary outcome. The one significant result was a small gain on a naming test that the authors thought might reflect practice effects.[7] They recommended that future studies investigate higher doses.
A 2024 trial gave 61 patients either a CBD-dominant extract with a small amount of THC, or placebo, for two weeks. The mean dose was about 192 mg CBD and 6.4 mg THC daily.
Overall motor symptoms improved in both groups — but the difference between treatment and placebo wasn’t significant.[8]
One secondary finding was more encouraging: objective accelerometer measurements showed greater improvement in rest tremor with the extract. Isolated secondary findings need replication, though, particularly when a trial’s main result is negative. And sleep, cognition and activities of daily living all favoured placebo, with mild adverse effects more common on the extract.
In August 2026 a further trial tested a commercial cannabis oil in 101 patients with Parkinson’s and chronic pain, at a final dose of roughly 44 mg CBD and 1 mg THC daily over nine weeks. It was generally safe. It didn’t improve pain, or any other non-motor symptom measured, compared with placebo.[9] The researchers called for larger studies using higher concentrations.
What do patients report?
Surveys tell a more positive story than the trials, though they can’t tell us whether cannabis caused the improvements.
In a US survey of 1,064 people with Parkinson’s, about a quarter had used cannabis in the previous six months — mostly for anxiety, pain and sleep — and many reported some relief.[10] But nearly a quarter of users had stopped in the same period, most commonly because it didn’t help, and many didn’t know the cannabinoid content of what they were taking.
Useful for understanding what patients are trying. Not evidence that any particular product works.
What about slowing the disease?
Laboratory and animal work has found cannabinoids protective of dopamine-producing neurons, with plausible mechanisms involving inflammation and oxidative stress. That’s a real line of research.
Nothing in humans supports it. No trial has shown CBD slows Parkinson’s, and none has been designed to look. Anyone claiming it prevents or delays the disease is going beyond what’s known.
If you’re considering it
Talk to your neurologist first. Parkinson’s medication is finely balanced, and CBD affects how the body processes a number of drugs.
Be clear which you’re trying. A CBD product and a THC-containing cannabis product have different evidence behind them and different trade-offs. They aren’t interchangeable.
Retail doses are far below those used in the high-dose study. It gave hundreds to thousands of milligrams daily under supervision. A shop-bought oil offering 25 mg is not a small version of that.
High doses need monitoring. Five of the 13 participants taking 20–25 mg/kg daily developed raised liver enzymes. Blood tests can detect that, and it may mean reducing or stopping the dose — a reason to involve a doctor.
Watch for blood pressure effects. Parkinson’s often comes with orthostatic hypotension, and CBD may lower blood pressure further.
Where this leaves it
The controlled trials have been disappointing. Purified CBD hasn’t beaten placebo for routine motor symptoms or REM sleep behaviour disorder. CBD-dominant products containing small amounts of THC haven’t improved cognition, overall motor symptoms, pain or other non-motor symptoms — though one produced an encouraging secondary tremor finding in a trial whose main result was negative.
Two things keep that from being the end of the question. Nobody has run a blinded motor trial at the exceptionally high doses used in the 2020 open-label study — though those doses also produced frequent side effects and liver-enzyme elevations. And patients continue to report benefits, mostly for anxiety, sleep and pain rather than movement.
Those reports may reflect expectation, selection effects or differences between products. They may also point to outcomes the trials haven’t captured well. Only better controlled studies can separate those possibilities.
None of this is medical advice. Parkinson’s needs specialist care, and nothing here substitutes for it.
For more, see our guides to CBD and drug interactions and what the research actually shows, or browse Health Conditions.
References
- Zuardi AW, Crippa JA, Hallak JE, et al. Cannabidiol for the treatment of psychosis in Parkinson’s disease. Journal of Psychopharmacology. 2009;23(8):979–983. doi:10.1177/0269881108096519
- Chagas MH, Eckeli AL, Zuardi AW, et al. Cannabidiol can improve complex sleep-related behaviours associated with rapid eye movement sleep behaviour disorder in Parkinson’s disease patients: a case series. Journal of Clinical Pharmacy and Therapeutics. 2014;39(5):564–566. doi:10.1111/jcpt.12179
- Chagas MH, Zuardi AW, Tumas V, et al. Effects of cannabidiol in the treatment of patients with Parkinson’s disease: an exploratory double-blind trial. Journal of Psychopharmacology. 2014;28(11):1088–1098. doi:10.1177/0269881114550355
- de Almeida CMO, Brito MMC, Bosaipo NB, et al. Cannabidiol for rapid eye movement sleep behavior disorder. Movement Disorders. 2021;36(7):1711–1715. doi:10.1002/mds.28577
- de Faria SM, de Morais Fabrício D, Tumas V, et al. Effects of acute cannabidiol administration on anxiety and tremors induced by a simulated public speaking test in patients with Parkinson’s disease. Journal of Psychopharmacology. 2020;34(2):189–196. doi:10.1177/0269881119895536
- Leehey MA, Liu Y, Hart F, et al. Safety and tolerability of cannabidiol in Parkinson disease: an open label, dose-escalation study. Cannabis and Cannabinoid Research. 2020;5(4):326–336. doi:10.1089/can.2019.0068
- Mitarnun W, Kanjanarangsichai A, Junlaor P, et al. Cannabidiol and cognitive functions/inflammatory markers in Parkinson’s disease: a double-blind randomized controlled trial at Buriram Hospital (CBD-PD-BRH trial). Parkinsonism & Related Disorders. 2025;135:107841. doi:10.1016/j.parkreldis.2025.107841
- Liu Y, Bainbridge J, Sillau S, et al. Short-term cannabidiol with Δ-9-tetrahydrocannabinol in Parkinson’s disease: a randomized trial. Movement Disorders. 2024;39(5):863–875. doi:10.1002/mds.29768
- Kubota GT, Parmera JB, Deltreggia M, et al. Cannabis-based oil for pain and other non-motor symptoms in Parkinson’s disease: a randomized controlled trial. Movement Disorders. 2026. doi:10.1002/mds.70449
- Feeney MP, Bega D, Kluger BM, et al. Weeding through the haze: a survey on cannabis use among people living with Parkinson’s disease in the US. npj Parkinson’s Disease. 2021;7:21. doi:10.1038/s41531-021-00165-y
About this article
Substantially rewritten in August 2026, consolidating our earlier reporting on CBD and Parkinson’s. This update adds the randomised trials published since, separates the evidence for CBD alone from that for THC-containing cannabis, and removes claims about preventing or delaying the disease. With earlier reporting by Derek Johnson and Colby McCoy.
