In a double-blind trial, neither the participants nor the researchers who deal with them know who is getting the treatment and who is getting the comparison. ClinicalTrials.gov calls this masking or blinding (ClinicalTrials.gov). Some trials go further: “triple-blind” or “quadruple-masked” means that outcome raters or analysts are kept in the dark too.
Blinding matters because hope and suspicion change how people feel and how staff score them. Many psilocybin trials are labelled double-blind, including a 59-person trial against escitalopram (Carhart-Harris et al., 2021) and a 233-person trial in treatment-resistant depression (Goodwin et al., 2022).
With psychedelics the label can promise more than it delivers. In the 2026 EPISODE trial, described as triple-blind, 86% of participants correctly identified the higher dose (Mertens et al., 2026). Researchers call this functional unblinding and argue it probably inflates effect sizes (Muthukumaraswamy et al., 2021). A double-blind label is a design choice, not proof that the blind held.
Sources
- ClinicalTrials.gov: Learn About Studies
- Mertens et al., JAMA Psychiatry, 2026
- Muthukumaraswamy et al., 2021
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