UMBRAA Framework Targets Blinding Failures in Psilocybin Trials

A Viewpoint published online recently in JAMA Psychiatry proposes a new blinding framework called UMBRAA (unidentifiable multidrug blinding with reduced, authorized awareness) to address years of failed masking in high-dose psilocybin trials.¹

Correct treatment identification in psilocybin trials now exceeds 90%, even against active placebos selected to produce noticeable effects, far above the roughly 60% rate seen in antidepressant trials.¹ Many investigators have concluded effective masking of high-dose psychedelics is not achievable and have called for a shift toward comparative efficacy designs instead.¹ Josh D. Woolley, MD, PhD, corresponding author of the Viewpoint and a member of the Department of Psychiatry and Behavioral Sciences at the University of California, San Francisco, argues the field has abandoned the problem before sufficiently aggressive approaches were tried.

"The reason we do masking is because people have ideas about how the treatment will help them, which is totally okay," Woolley said. "But if they can tell what they get, expectancy is differentially activated.”

Why Active Placebos Fail to Mask Psilocybin's Effects

A 25 mg dose of psilocybin produces perceptual distortions, ego dissolution, and pronounced emotional swings lasting 4 to 6 hours.¹ Early comparators such as niacin and diphenhydramine never plausibly mimicked this profile, and more recent proposals, including tetrahydrocannabinol (THC), salvinorin A, and dextromethorphan (DXM), still fail to reproduce psilocybin's full experiential breadth as single agents.¹ Woolley and colleagues note regulatory agencies have held active placebos to an outpatient tolerability threshold irrelevant to a single supervised administration, since a 25 mg psilocybin dose routinely requires 8-hour supervised sessions, intensive monitoring, and postdosing driving restrictions.¹

DXM illustrates a second problem beyond its incomplete resemblance to psilocybin. At dissociative doses, its N-methyl-d-aspartate (NMDA) antagonism can produce rapid-acting antidepressant effects similar to ketamine, so investigators cannot rule out an antidepressant effect from a single high dose in depression trials. Woolley and colleagues argue expecting a mild comparator to mask this experience is not a cautious choice but a methodological mismatch that all but guarantees unmasking.

UMBRAA Combines Multidrug Comparators with Authorized Disclosure

UMBRAA proposes combining agents from distinct mechanistic classes, potentially a stimulant, sedative, anticholinergic, and cannabinoid, chosen to avoid psilocybin's primary 5-hydroxytryptamine receptor 2A (5-HT2A) mechanism and to produce an intense, unfamiliar profile.¹ Woolley and colleagues cite a 19th-century precedent in which combining hashish with strong coffee produced classically psychedelic experiences, including visions and ego dissolution, effects neither substance reliably produces alone.¹ Combining classes can also extend the duration and offset dose-limiting adverse effects of individual agents; stimulants, for example, can counteract sedative-induced sleep and augment perceptual effects, and hallucinations occur in up to 4.7% of zolpidem-treated individuals, rising to nearly 8% when stimulants are added.¹

The second element pairs this multidrug approach with what Woolley and colleagues term authorized incomplete disclosure, an extension of standard blinding in which participants consent in advance to not being told certain design details, such as the number of treatment arms.²

"We argue there are some other elements of the trial design that you can ethically not disclose, for example, the number of treatment arms in the study," Woolley said. "If you tell people you're withholding that information, they can consent."

Watch part 1 of the interview with Woolley here: UMBRAA Framework Aims to Fix Blinding Failures in Psychedelic Trials

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

References

1. Yang KH, Heifets BD, Krystal A, et al. The case for more aggressive masking in psychedelic trials. JAMA Psychiatry. Published online September 16, 2026. doi:10.1001/jamapsychiatry.2026.2858

2. Matvey M, Kelley DP, Bradley ER, Chiong W, O'Donovan A, Woolley J. Modifying informed consent to help address functional unmasking in psychedelic clinical trials. JAMA Psychiatry. 2025;82(3):311-318. doi:10.1001/jamapsychiatry.2024.4312