Safety, Tolerability, and Preliminary Efficacy of Psilocybin Oral Solution in Adults With Generalized Anxiety Disorder

This Phase IIa, placebo-controlled, double-blind trial (n=50) will study the safety, tolerability, and preliminary efficacy of a 3 mg dose of psilocybin (oral solution) in adults with generalised anxiety disorder (GAD).

Conducted by Queen’s University in Canada and sponsored in collaboration with Diamond Therapeutics, this study consists of three stages: a 4-week screening period, a 4-week open-label phase (where all participants receive daily psilocybin), and a 4-week double-blind phase where only those who show a 50% or greater reduction in anxiety symptoms will be randomly assigned to continue with psilocybin or switch to a placebo.

The primary goal is to assess adverse events and tolerability, while secondary measures include reductions in anxiety symptoms, tracked via standard scales such as the Hamilton Anxiety Rating Scale (HAM-A). Participants are adults aged 18–60 diagnosed with GAD and not currently on daily anxiolytic (anti-anxiety) medication. The study will also collect cognitive data and neurophysiological measures (like EEG) across the treatment period. The trial is expected to run from May 2025 to August 2026.

Trial Details

This Phase 2a clinical trial is designed to evaluate the safety, tolerability, and preliminary efficacy of a 3 mg dose of psilocybin oral solution for the treatment of Generalized Anxiety Disorder (GAD). The study consists of three sequential phases: Screening Phase (up to 4 weeks), Open-label Run-in Phase (4 weeks), Double-blind Treatment Phase (4 weeks) Screening Phase During the Screening Visit, participants will provide informed consent and undergo a comprehensive medical evaluation, including an abbreviated psychiatric assessment, to determine eligibility. To qualify, patients must have a clinician-rated Hamilton Anxiety Rating Scale (HAM-A) score ≥14. Additionally, participants must not be on regular anxiolytic treatment or must have discontinued such treatment at least 4 weeks prior to the start of the Open-label Run-in Phase. Open-label Run-in Phase Eligible patients will proceed to the 4-week Open-label Run-in Phase. During this phase, patients will attend four weekly clinic visits, supplemented by weekly remote contacts (via phone or email). At different timepoints during the OL Run-in Phase, participants will complete safety assessments, undergo cognitive testing and EEG and other patient reported outcomes (PROs). Double-blind Treatment Phase Participants who demonstrate a treatment response during the Open-label Phase-defined as a ≥50% reduction in GAD-7 score from baseline-will be randomized 1:1 to receive either psilocybin oral solution or placebo at the Double-blind Baseline Visit. Patients not meeting the response criteria will undergo End-of-Treatment (ET) procedures at this visit. At different timepoints during the DB Treatment Phase, participants will complete safety assessments, undergo cognitive testing and EEG and other patient reported outcomes (PROs). Completion of the End of Treatment (ET) phase will be 2 weeks to further assess safety and PROs.

Trial Number NCT06969170

Data attribution

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