High doses of delta-9-tetrahydrocannabinol (THC) have been reported by some people to produce experiences resembling those of classic psychedelic drugs. But how high the dose must be and what the experience looks like have been poorly mapped. Now a new pilot study offers a first insight into how THC and psilocybin relate to each other under controlled trial conditions.
Study Design
The short study compared acute effects of THC and psilocybin in the same type of controlled trial setting used in classic clinical trials with psychedelic drugs. Four healthy adults (ages 31–47, three female) received placebo, 25 mg psilocybin and 25 mg THC orally. Two of the participants also received 50 mg THC in a double-blind, placebo-controlled, within-subject crossover study.
THC was given either as synthetic THC (dronabinol) or as a whole-plant extract with 89.9% THC. Subjective effects, cardiovascular function and safety were followed throughout each session. After each trial, participants were asked to state which drug they believed they had received.
25 mg Produced a Similar Experience to Psilocybin
The results showed that 25 mg THC in both forms produced an experience similar to 25 mg psilocybin. Dronabinol was interpreted as a classic hallucinogen by both a participant with no prior psychedelic experience and a participant with such experience.
Mistaken Despite an Unusual Dose
The researchers note that these preliminary data suggest that 25 mg of pure, synthetic THC taken orally can be mistaken for a classic hallucinogen, and that orally administered THC can elicit an experience resembling that of classic psychedelic drugs, even in a typical clinical trial setting. Although the study has a small sample, it offers important insights into the psychological effects of THC and psilocybin.
Set and Setting Matter
A central conclusion is that the setting and expectations play a major role in how psychoactive drugs are experienced. Even for high-dose THC, the environment and expectations appear to markedly shape the experience.
Source:
Pilot study comparing the effects of high dose THC to high dose psilocybin and placebo in the set and setting of a classic psychedelic therapy session — Psychopharmacology (Berl), 2026. DOI: 10.1007/s00213-026-07138-0
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