Journal of psychopharmacology (Oxford, England)Sep 8, 2026

Psychedelic therapy shows no lasting effects: Review of controlled studies from 1965 to 1977

Psychedelic Science Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Sep 9, 2026

Abstract

Most early controlled studies of psychedelic therapy show no durable improvements in patients' conditions beyond a few weeks.

Eleven controlled studies conducted in the U.S. and Canada between 1965 and 1977 were reviewed.
These studies aimed to treat individuals with alcohol and opioid use disorders, as well as psychoneuroses.
Despite methodological heterogeneity, the studies largely adhered to the regulatory standards of their time.
Common methodological issues such as blinding and active control conditions were addressed in these early trials.
Patient selection may benefit from focusing on non-chronic conditions.
There are concerns regarding the exclusive emphasis on mystical experiences as the main mechanism of action.

Simplified

Common wisdom in the psychedelic literature suggests that early controlled trials of psychedelic therapy were methodologically flawed. In this review we challenge this view and discuss 11 controlled studies that were conducted in the United States and Canada between 1965 and 1977 to evaluate psychedelic (peak) therapy for individuals suffering from alcohol and opioid use disorder and psychoneuroses. We provide a narrative review of the designs, methods, settings, treatment issues and results and show that these studies already adhered quite well to the regulatory and evidentiary standards of their time. These early psychedelic trials tried to effectively address common methodological problems that still threaten the validity of contemporary psychedelic clinical trials (e.g., regarding blinding and active control conditions). Our review indicates that despite a significant heterogeneity in the methods and research designs, most early controlled studies converge on the same conclusion: there are no durable improvements in the condition of patients treated with psychedelic therapy beyond a few weeks. We discuss implications for contemporary psychedelic science in terms of (a) patient selection (i.e., better prospects for non-chronic conditions), (b) the problems with a single-sided focus on mystical experiences as the primary mechanism of action, (c) the positive afterglow as a therapeutic window of opportunity and (d) the need for a strong psychotherapeutic framework to induce sustained therapeutic effects.

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Psychedelic therapy shows no lasting effects: Review of controlled studies from 1965 to 1977

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