Nightly CBD in Insomnia: Cognitive Null Results and Subjective Improvements Differed
Two weeks of nightly CBD did not significantly change tested daytime cognitive performance compared with placebo in a small insomnia trial. Some subjective ratings improved, but feeling clearer-headed should not be reported as an objective cognitive-performance improvement.
A short parallel-group pilot
Thirty participants with primary insomnia were assigned to 150 mg CBD or placebo, 15 per group. A placebo run-in preceded two weeks of blinded nightly dosing. The study used a sublingual preparation approximately an hour before bed.
Testing covered attention, executive function, reasoning, information processing, working memory and episodic memory. These are specific daytime assessments, not an on-road driving test or proof that all activities are unaffected.
The outcome measures diverged
The trial did not detect a treatment-related cognitive deficit across the assessed domains. Participants receiving CBD reported greater calmness, clear-headedness and coordination over the study, while dry mouth was also reported more often.
Subjective coordination and a measured performance task are different endpoints. Improvements in one cannot be substituted for significant improvement in the other. Similarly, a nonsignificant cognitive contrast does not prove exact equivalence between treatments.
What remains uncertain
Fifteen participants per group and a two-week exposure provide limited information about small effects, uncommon adverse events or longer-term use. The findings also concern people with primary insomnia rather than a representative sample of all CBD users.
The trial’s contribution is reassurance within a defined protocol, alongside separate subjective and tolerability observations. It does not establish an optimal insomnia treatment, a universal next-day driving clearance or identical results for products that also contain THC.
Related: Interpreting cannabinoid concentrations and functional effects.
Primary research
The effect of nightly use of 150 mg cannabidiol on daytime neurocognitive performance in primary insomnia: a randomized controlled pilot trial. Psychopharmacology (2024).
