A placebo-controlled trial has shown that a single dose of psilocybin, the active ingredient in magic mushrooms, leads to rapid and lasting reductions in obsessive-compulsive disorder symptoms among treatment-resistant patients. The effects persisted for at least 12 weeks in participants who had not responded to conventional therapies. Researchers highlight the potential of this psychedelic for mental health treatment, though larger studies are needed.
Obsessive-compulsive disorder (OCD) affects 1 to 3 per cent of people and involves obsessive thoughts and compulsive habits that can overwhelm daily life. Standard treatments, such as talking therapies and antidepressants, fail to help between 40 and 60 per cent of patients.
In the first randomised, placebo-controlled trial of psilocybin for OCD, Christopher Pittenger at Yale School of Medicine and colleagues recruited 28 adults who had experienced the condition for an average of two decades and had tried at least two prior treatments unsuccessfully. Participants' symptoms were assessed using a standard scale scoring from 0 to 40. They were randomly assigned to receive either a single oral dose of psilocybin at 0.25 milligrams per kilogram of body weight or 250 milligrams of niacin as a placebo.
The psilocybin dose induced a psychedelic experience, involving changes in perception, thoughts, and emotions. Within 48 hours, the 14 participants who received psilocybin saw their symptom scores drop by an average of 9.76 points, while the niacin group showed no significant change. One week later, about 70 per cent of the psilocybin group maintained a roughly 35 per cent reduction in symptoms, with benefits still evident at the 12-week follow-up.
"The speed and durability of the improvement seen after a single dose of psilocybin are remarkable," says Alex Kwan at Cornell University in Ithaca, New York. David Nutt at Imperial College London, who was not involved in the study, notes, "It’s definitely better and faster than other medications for OCD."
Psilocybin may enhance brain plasticity, making rigid thoughts less dominant, or recalibrate brain networks involved in rumination. However, the exact mechanism remains unclear. The trial reported one participant with pre-existing suicidal thoughts who briefly planned self-harm, underscoring the need for clinical safeguards. Blinding was a challenge, as most participants could identify the active drug despite efforts to mimic effects with niacin. Larger trials are required to confirm efficacy, optimal dosing, and safety profiles.
This research builds on psilocybin's promise for conditions like depression, but experts emphasise caution in its medical application.
