Josh D. Woolley, MD, PhD, professor of psychiatry and behavioral sciences, University of California, San Francisco.

Josh D. Woolley, MD, PhD

A Viewpoint published in JAMA Psychiatry proposes multidrug active placebos to mask high-dose psychedelics in clinical trials.

Correct treatment guessing exceeds 90% in high-dose psychedelic trials, compared with approximately 60% in antidepressant trials.

 This makes it difficult to separate a drug's pharmacological effects from participants' own expectations.

“The doses used in these trials are high doses,” said author Josh D. Woolley, MD, PhD, professor of psychiatry and behavioral sciences, University of California, San Francisco, in an interview with 

. “People have big experiences, with visual changes and intense experiences of bliss, unity, and feeling one with the universe. In most trials, two-thirds of people say it's among the top 5 most meaningful experiences of their life."

UMBRAA Framework Aims to Fix Blinding Failures in Psychedelic Trials

Masking Failure in High-Dose Psychedelic Trials

A 25-mg dose of psilocybin produces a profound alteration of consciousness lasting 4 to 6 hours, including perceptual distortions, ego dissolution, and powerful emotional swings participants often rate among the most significant experiences of their life. Earlier comparators, including niacin and diphenhydramine, produced no plausible psychedelic-like experience.

Woolley said participants in some early trials either had a profound mystical experience or, on niacin, simply became itchy. Newer single-agent options such as THC, salvinorin A, and dextromethorphan carry a recognizable pharmacological fingerprint experienced participants can identify.¹ Dextromethorphan poses an additional confound: at dissociative doses, N-methyl-d-aspartate receptor antagonism can produce rapid-acting antidepressant effects overlapping with ketamine, complicating its use as a comparator in depression trials.¹

Unlike an SSRI trial, where a participant might infer treatment assignment gradually from a side effect such as sexual dysfunction, unmasking in psychedelic trials happens abruptly and completely on the dosing day, with therapists present throughout administration and integration.

UMBRAA: Multidrug Blinding With Incomplete Disclosure


UMBRAA (unidentifiable multidrug blinding with reduced, authorized awareness) is a proposed active placebo strategy that combines agents from distinct mechanistic classes, such as a stimulant, sedative, anticholinergic, and cannabinoid, with incomplete disclosure of trial arm composition to improve masking in high-dose psychedelic trials.

Why has masking failed in high-dose psychedelic trials?


A 25-mg psilocybin dose produces perceptual distortions, ego dissolution, and emotional intensity no conventional comparator can replicate, letting participants correctly guess their assignment more than 90% of the time.

How would UMBRAA manage the added safety risk of combining multiple drugs?


The authors propose repurposing FDA-approved agents and applying monitoring standards already used in psychedelic trials, treating the resulting disorientation as the intended experiential target rather than an adverse event.

Woolley and colleagues propose combining agents from distinct mechanistic classes, such as a stimulant, sedative, anticholinergic, and cannabinoid, chosen to avoid overlap with psilocybin's primary serotonin 2A receptor mechanism.¹ They term this framework UMBRAA, for unidentifiable multidrug blinding with reduced, authorized awareness. Combining classes can extend the comparator's duration and offset dose-limiting adverse effects of individual agents; stimulants can counteract sedative-induced sleep while amplifying perceptual effects, and hallucinations occur in up to 4.7% of zolpidem-treated patients, rising to nearly 8% with stimulant coadministration.¹

The approach pairs this pharmacological strategy with incomplete disclosure: participants and, ideally, staff learn only they may receive psilocybin alongside 1 or more additional agents, without being told the total number of trial arms.¹ The authors acknowledge cardiovascular instability and respiratory depression as risks of multidrug combinations, proposing these be managed by repurposing FDA-approved drugs and applying monitoring standards already required in many psychedelic trials.¹ They frame the resulting disorientation and perceptual disturbance not as complications but as the intended experiential profile.

"Psilocybin is quite tolerable, and the safety is pretty high, which is true, but it comes in the setting of a very intensive delivery model," Woolley said. "Patients arrive for preparation and screening, then stay all day with 2 providers in the room, vital sign monitoring, and an MD on call. It's not outpatient. It's a procedure."

Editor’s note: A reported disclosure for Woolley includes Eli Lilly and Company 

Yang KH, Heifets BD, Krystal A, et al. The case for more aggressive masking in psychedelic trials. 

Taylor JJ, Szigeti B, Silverberg ND, Ahmadzad-Asl M, Kare M, Webler R, Orsini DK, Rosenblat JD, Bschor T, Baethge C, Sinyor M, Nicholson TR, Wager TD, Burke MJ. Measuring and appraising placebo effects in clinical trials: contemporary challenges and approaches in psychiatry. Lancet Psychiatry. 2026 May;13(5):426-440. 

doi: 10.1016/S2215-0366(26)00018-0. PMID: 41997697; PMCID: PMC13326907.

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In his paper, Josh D. Woolley, MD, PhD, proposes multidrug active placebos and limited disclosure to finally mask high-dose psilocybin trials.

Josh D. Woolley, MD, PhD

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