Summary: A Phase 2 randomized clinical trial from the Karolinska Institute found that a single 25 mg dose of psilocybin, combined with structured psychotherapeutic support, produced a rapid, statistically significant, and clinically meaningful reduction in symptoms among people with recurrent major depression.
The antidepressant effect was detectable as early as day two by self-report, and 53% of participants in the psilocybin group reached clinical remission at six weeks. The treatment was generally well tolerated, though two participants experienced severe persistent anxiety requiring medical attention. The study also highlights ongoing methodological challenges in psychedelic research, especially effective blinding.
Key Facts
- Rapid and sustained symptom reduction: By day 8—the primary outcome—the psilocybin group showed an average 9.7‑point reduction on the MADRS depression scale versus 2.4 points in the active placebo group, a clinically meaningful difference that remained detectable through day 42.
- High remission rate at six weeks: 53% of participants who received psilocybin achieved full clinical remission at six weeks, compared with 6% in the active placebo group.
- One‑year outcomes uncertain: The same 53% of the psilocybin group were still in remission at day 365, but no statistically significant difference between groups persisted at one year because many placebo participants recovered over time.
- Blinding remains a challenge: Despite using niacin as an active placebo to produce noticeable physical sensations, nearly all participants correctly guessed their assignment, raising the possibility that expectations influenced outcomes.
Source: Karolinska Institute
Background: Major depressive disorder is a leading public health concern. Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants, but many patients do not respond or experience delayed onset of benefit and bothersome side effects. Psilocybin, the primary psychoactive compound in “magic mushrooms,” has shown promise as a rapid-acting antidepressant in earlier research, though most prior trials focused on cancer-related depression or treatment‑resistant cases. This Phase 2 trial evaluated whether psilocybin could produce meaningful improvement in a broader group of people with recurrent major depression.
Thirty‑five adults aged 20 to 65 with moderate to severe recurrent depression were randomized to a single 25 mg oral dose of psilocybin (n=17) or an active placebo of 100 mg niacin (n=18). All participants received five scheduled psychotherapeutic support sessions: preparatory sessions before dosing, support during the dosing session, and integration sessions after dosing. During the dosing session participants reclined, wore an eye mask, and listened to a prepared music program through headphones to encourage inward focus.
Depressive symptoms were assessed with the clinician‑rated Montgomery–Åsberg Depression Rating Scale (MADRS) at baseline and on days 8, 15, 42 and 365. Monthly self-reports using MADRS‑S and other measures of functioning, quality of life, and anxiety were collected throughout the 12‑month follow-up.
Eligibility required a baseline MADRS total of at least 22. The primary endpoint was the between‑group difference in MADRS change from baseline to day 8. At that time point, the psilocybin group’s MADRS score fell by an average of 9.7 points versus a 2.4‑point drop in the niacin group, yielding a model‑estimated between‑group difference of 7.3 points in favor of psilocybin. This difference was statistically significant and considered clinically meaningful, and it persisted at day 15 and day 42.
Participants’ self‑rated MADRS‑S scores showed an antidepressant effect as soon as day 2, with group differences maintained through about three months on secondary outcomes. At six weeks, 53% of those given psilocybin met criteria for remission versus 6% in the active placebo arm. By one year the proportion in remission remained 53% in the psilocybin group, but group differences were no longer statistically significant because many placebo participants improved over time.
Adverse events were mostly transient and mild to moderate. Two participants in the psilocybin group experienced persistent severe anxiety that required additional medical care; no drug‑related serious adverse events were reported. Investigators emphasize that psilocybin treatment is not risk‑free and that some patients will require extra clinical support during and after dosing.
The study also underlines a major methodological issue for psychedelic trials: the difficulty of maintaining blinding. Because psilocybin produces strong, distinct subjective effects, participants and staff often infer treatment assignment. In this trial nearly all participants correctly guessed their group, which could inflate perceived treatment benefit through expectation effects. The authors call for further research that examines how expectations and blinding influence outcomes and for larger trials to determine optimal dosing and maintenance strategies.
Planned secondary analyses include PET imaging and biomarker studies using blood and cerebrospinal fluid samples collected before and after dosing. Preclinical data suggest psychedelics may promote synaptic growth and change brain network interactions implicated in depression; these biological measures will help test whether psilocybin alters synaptic density or connectivity in humans.
The trial was conducted by Karolinska Institutet in collaboration with the Brain Stimulation Clinic at Northern Stockholm Psychiatry. Funding was provided by Norrsken Mind and the Swedish Research Council. One study leader reports a personal honorarium from an industry company.
Facts about the MADRS:
The Montgomery–Åsberg Depression Rating Scale (MADRS) rates depressive symptom severity from 0 to 60, with higher scores indicating more severe depression:
* 0–12 points: no depression or very mild depression
* 13–19 points: mild depression
* 20–34 points: moderate depression
* 35–60 points: severe depression
Key Questions Answered:
A: Based on these results, yes. Traditional SSRIs often take several weeks to produce noticeable benefit, whereas participants here reported symptom improvement as early as two days after a single psilocybin dose.
A: Psilocybin is not risk‑free. Most adverse effects in this trial were mild and transient, but two participants experienced severe persistent anxiety that required medical care. Clinical supervision and appropriate screening are essential.
A: Probably not for most people. Although over half of the psilocybin group remained in remission at one year, the long‑term durability of a single dose is uncertain. The authors emphasize that repeated treatments or adjunctive strategies may be needed to prevent relapse.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The full journal paper was reviewed.
- Additional context was added by the editorial staff.
About this psychopharmacology and depression research news
Author: Press Office
Source: Karolinska Institute
Contact: Press Office – Karolinska Institute
Image: The image is credited to Neuroscience News
Original Research: Open access. “Acute and Late Effects of Psilocybin on Symptoms in Major Depression: a randomized clinical trial” by Hampus Yngwe et al., JAMA Network Open. DOI: 10.1001/jamanetworkopen.2026.12589
Abstract
Acute and Late Effects of Psilocybin on Symptoms in Major Depression: a randomized clinical trial
Importance
Psilocybin has been proposed as a rapid‑acting antidepressant (onset <2 weeks) with prolonged effects (>6 weeks). However, randomized clinical trial evidence in a broader major depressive disorder (MDD) population remains limited.
Objective
To evaluate short‑term and long‑term antidepressant effects of psilocybin therapy in people with MDD.
Design, Setting, and Participants
This double‑blind, placebo‑controlled randomized clinical trial enrolled adults with moderate to severe recurrent MDD at the Northern Stockholm Psychiatric Clinic between January 26, 2021, and February 19, 2024. Statistical analysis was performed from February 20, 2024, to June 20, 2025.
Interventions
Participants received a single 25 mg dose of psilocybin or an active placebo (100 mg niacin) and five psychotherapeutic support sessions over 17 days.
Main Outcomes and Measures
The primary end point was the between‑group difference in change in MADRS score from baseline to day 8. Secondary end points included MADRS at days 15, 42, and 365, monthly self‑reports (MADRS‑S), and measures of disability, quality of life, and anxiety across 12 months.
Results
Thirty‑five participants (21 female; mean age 41.0 years) were randomized (17 psilocybin, 18 niacin). The trial met its primary end point: the model‑estimated mean between‑group difference in MADRS change at day 8 favored psilocybin (−7.27; 95% CI, −12.89 to −1.65; P = .01). Significant between‑group differences persisted at days 15 and 42 but were not significant at day 365. Self‑reported MADRS‑S showed a significant advantage for psilocybin beginning at day 2 and lasting more than three months on secondary measures. Most treatment‑emergent adverse events were mild to moderate and transient; two participants reported persistent severe anxiety requiring medical attention; no drug‑related serious adverse events were reported.
Conclusions and Relevance
A single 25 mg dose of psilocybin with psychological support produced rapid antidepressant effects detectable by day 2 and sustained for over three months on some measures. Psilocybin was generally well tolerated, though a subset of participants required additional care for anxiety. These findings support further research into repeated dosing, maintenance strategies, and the biological mechanisms underlying psilocybin’s antidepressant effects.
Trial Registration
ClinicalTrials.gov Identifier: NCT04630964