A 12-week randomized trial found 26 mg/day sublingual CBD was safe in Parkinson's disease but did not significantly improve memory or motor symptoms, with only naming scores showing improvement.
Parkinson's patients considering CBD, neurologists, clinical trial designers
26 mg/day CBD safe in Parkinson's but largely ineffective at this low dose
What the researchers found
Among 51 Parkinson's patients completing the trial, low-dose CBD (26 mg/day) was safe with no serious side effects. The only significant cognitive improvement was in MoCA naming scores. Delayed recall (primary outcome), language, inflammatory markers, and motor symptoms showed no differences between CBD and placebo groups.
Why it matters
This is one of the few rigorous RCTs testing CBD in Parkinson's disease. While the results are largely negative at this dose, the safety data supports exploration of higher doses in future trials.
The numbers in context
60 randomized (27 CBD, 24 placebo completed). Mean CBD dose: 26 mg/day, THC: 1.2 mg/day. CBD detected in serum at mean 2 ng/mL. No THC detected. Only naming score improved (mean difference: 0.37, 95% CI: 0.01-0.73).
How the study worked
Double-blind randomized controlled trial of 60 Parkinson's patients (51 completed) comparing 12 weeks of sublingual CBD-enriched product (101.9 mg/mL CBD, 4.8 mg/mL THC) to placebo, measuring cognitive, motor, and inflammatory outcomes.
What this study cannot tell us
Very low CBD dose (26 mg/day) may be below therapeutic threshold. Small sample after dropout. 12-week duration may be too short. Blood levels suggest poor bioavailability. CBD-enriched product contained trace THC.
How to read the evidence
Rigorous double-blind RCT, but small sample, high dropout, and very low dose limit ability to draw definitive conclusions about CBD efficacy.
When this study was published
2025 randomized controlled trial from Buriram Hospital, Thailand.
The bigger picture
The Parkinson's community has enormous interest in CBD, but this trial suggests very low doses may not be sufficient. The safety profile is encouraging for future dose-escalation studies.
Questions still open
- Would higher CBD doses produce meaningful cognitive benefits? Is sublingual the optimal route for Parkinson's patients? How long would treatment need to continue for effects to emerge?
Common questions
Does CBD help with Parkinson's disease?
Is CBD safe for Parkinson's patients?
Read the original research
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, 135, 107841
Citation
Mitarnun, Witoon; Kanjanarangsichai, Auempa; Junlaor, Panomporn; Kongngern, Lisa; Mitarnun, Wenika; Pangwong, Wilasinee; Nonghan, Pawarin. (2025). 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, 135, 107841. https://doi.org/10.1016/j.parkreldis.2025.107841
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