Evaluation of the Effects of Different Doses of Ayahuasca on Intelligence and Verbal Memory in Healthy Volunteers

Background: Observational studies with ritual ayahuasca users suggest that experienced users tend to have better cognitive performance, while novice users may experience transient impairments, particularly in working memory. However, no randomized clinical trials have systematically evaluated the cognitive effects of ayahuasca in healthy volunteers. Procedures: This double-blind, randomized, placebo-controlled trial evaluated the effects of a single dose of ayahuasca on intelligence and verbal memory in 28 healthy volunteers. Participants were randomized to receive placebo (1.0 mL/kg) or ayahuasca at doses of 0.5, 1.0, or 1.5 mL/kg (n=7 per group). The Wechsler Abbreviated Scale of Intelligence and the Rey Auditory Verbal Learning Test were administered at baseline, 4 hours, and 21 days postadministration. Results: For intelligence, significant time effects were observed across multiple domains ( P <0.05), but no group × time interactions were detected. For verbal memory, significant time effects were observed for total learning, immediate recall, delayed recall, recognition, and total learning ( P <0.05). A significant group × time interaction was observed only for delayed recall ( P =0.006), with post hoc analysis revealing that the placebo performed better than the 0.5 mL/kg ayahuasca group at 4 hours ( P =0.006). No other interactions reached significance, and no effects persisted at 21 days. Conclusions: In this preliminary exploratory trial, we found no evidence that a single administration of ayahuasca produced significant or persistent changes in standardized measures of intelligence or verbal memory in healthy volunteers. These findings provide preliminary information regarding short-term tolerability and cognitive performance following controlled administration and may inform future adequately powered trials.