In brief
- A team from the University of Toronto reviewed 112 psychedelic clinical trials to determine if blinding—ensuring participants do not know whether they received the substance or a placebo—holds up in practice.
- In MDMA trials versus an inert placebo, more than 85% of participants guessed correctly; for psilocybin, LSD, and ayahuasca, the figure exceeded 90%.
- Only 29.5% of the analyzed studies formally measured whether the blind was maintained, despite it being a key factor in interpreting results.
One of the most debated aspects of psychedelic research has finally received a systematic assessment. A team led by Diana K. Orsini at the University of Toronto has published a review of 112 randomized clinical trials in JAMA Psychiatry to answer an uncomfortable question: do participants really not know whether they received the drug or a placebo? The answer, with few exceptions, is no.
What they found
The review covers trials on seven substances: ketamine (78 studies), LSD (17), psilocybin (11), MDMA (11), ayahuasca (2), DMT (2), and noribogaine (1). Of these, only 33—29.5%—formally measured the integrity of the blind, although 64 (57.1%) acknowledged the issue when listing their limitations. When measured, the data were stark: in MDMA trials with an inert placebo, more than 85% of participants correctly identified what they had taken. For psilocybin, LSD, and ayahuasca, the blinding failure rate exceeded 90% among both participants and the evaluators rating their condition.
Ketamine: The exception that proves the rule
Ketamine behaved differently, and the reason is revealing. Its trials assessed blinding even less—only 17.9%—but when they did, the blind held up significantly better if the comparator was midazolam, a sedative with perceptible subjective effects, rather than saline. In other words, the problem is not the substance being studied, but the act of comparing an intense experience with a pill that does absolutely nothing. Anyone can tell the difference, and from there, the expectation of receiving the active treatment can contaminate what is later measured as improvement.
What it implies
It is best to read this work for what it is: a methodological critique, not a verdict on whether psychedelics work. The authors do not claim that the observed efficacy is false; they point out that the tool used to measure it has a blind spot. They propose correcting this with standardized blinding measures, better-calibrated active comparators, and analyses that separate the pharmacological effect from participant expectations. This is not merely theoretical: it was exactly the argument the FDA used in 2024 when rejecting Lykos Therapeutics’ application for MDMA-assisted therapy for PTSD, and it is the same debate currently facing regulators in Australia, Canada, and Europe. Science scrutinizing itself is, ultimately, the best guarantee that what is eventually approved will stand the test of time. And for those who follow harm reduction from outside the lab, the reminder remains the same: every headline is backed by an experimental design and margins of uncertainty that are worth understanding. In that same spirit of methodological rigor, we recently published a piece on the MDMA analog without psychedelic effects, which seeks to bypass this very problem.
Source
- Orsini DK, et al. Blinding Integrity in Psychedelic Randomized Clinical Trials: A Systematic Review. JAMA Psychiatry, July 1, 2026.
Educational content written from a harm reduction perspective and with respect for individual freedom. It is not a substitute for advice from a healthcare professional and is not intended to encourage or condemn any drug use.
