A single dose of a 20:1 CBD:THC medicinal cannabis oil mildly impaired some memory functions while slightly improving mood in healthy adults.
Patients and prescribers considering CBD-dominant medicinal cannabis products, and regulators assessing safety profiles.
100mg CBD + 5mg THC mildly impaired memory but improved mood; 23% reported drowsiness
What the researchers found
A sublingual dose of CannEpil (100mg CBD, 5mg THC) impaired visuospatial working memory and delayed pattern recognition compared to placebo, but largely preserved mood. Participants felt more content and amicable about 2.5 hours after dosing. About 23% reported drowsiness between 3 and 6 hours post-dose.
Why it matters
As CBD-dominant products gain medical acceptance, knowing their acute cognitive effects is essential for safety, especially for users who drive or work.
The numbers in context
31 participants. 100mg CBD + 5mg THC sublingual dose. Contentedness (p<0.01) and amicability (p<0.05) improved at 2.5 hours. 23% reported drowsiness 3-6 hours post-dose.
How the study worked
Randomized, double-blind, placebo-controlled, within-subjects crossover trial with 31 healthy participants (16 female, 15 male) aged 21-58 over a two-week protocol.
What this study cannot tell us
Small sample (n=31) of healthy volunteers may not reflect patients with medical conditions. Single-dose design does not capture effects of repeated use. Only one CBD:THC ratio was tested.
How to read the evidence
Rigorous RCT design with double-blinding and crossover, but small sample size limits power.
When this study was published
Published in 2024.
The bigger picture
The mild cognitive effects alongside mood improvement reflects the tradeoff many medicinal cannabis users face. The lack of correlation between plasma levels and cognitive changes suggests individual differences may matter more than dose.
Questions still open
- Would tolerance develop to the cognitive effects with repeated dosing?
- Do patients with existing cognitive impairment experience greater effects than healthy volunteers?
Common questions
Does high-CBD cannabis oil affect your thinking?
Does CBD make you drowsy?
Read the original research
A randomised, placebo-controlled, double blind, crossover trial on the effect of a 20:1 cannabidiol: Δ9-tetrahydrocannabinol medical cannabis product on neurocognition, attention, and mood.
European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology, 82, 35-43
Citation
Manning, Brooke; Hayley, Amie C; Catchlove, Sarah; Stough, Con; Downey, Luke A. (2024). A randomised, placebo-controlled, double blind, crossover trial on the effect of a 20:1 cannabidiol: Δ9-tetrahydrocannabinol medical cannabis product on neurocognition, attention, and mood.. European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology, 82, 35-43. https://doi.org/10.1016/j.euroneuro.2024.02.002
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