Psychiatry · Medical Literature
Short-Term and Late-Term Effects of Psilocybin on Symptoms in Major Depression: A Randomized Clinical Trial.
Abstract
Psilocybin has been proposed as a rapid-acting antidepressant (onset 6 weeks), but evidence from randomized clinical trials remains limited, particularly in the broader major depressive disorder (MDD) population. To assess short-term and long-term antidepressant effects of psilocybin therapy in patients with MDD. This double-blind, placebo-controlled randomized clinical trial of participants diagnosed with moderate to severe recurrent MDD was conducted 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. Participants received a single dose of psilocybin (25 mg) or active placebo (niacin, 100 mg) and 5 psychotherapeutic support sessions during 17 days. The primary end point was between-group difference in change in Montgomery-Åsberg Depression Rating Scale (MADRS) score from baseline to day 8. Secondary end points included MADRS scores on days 15, 42, and 365, as well as monthly self-reports (MADRS-S) of depressive symptoms, disability, quality of life, and anxiety throughout the 365-day follow-up. The study included 35 participants (21 [60%] female; mean [SD] age, 41.0 [10.1] years) diagnosed with moderate to severe recurrent MDD, with 17 randomized to the psilocybin group and 18 to the niacin group. The study met its primary end point with a significant mean between-group difference (model estimated) in change in MADRS score on day 8 (-7.27; 95% CI, -12.89 to -1.65; P = .01) in favor of psilocybin. The between-group difference was significant also on days 15 (mean difference, -11.03; 95% CI, -16.65 to -5.42; P < .001) and 42 (mean difference, -8.33; -13.94 to -2.71; P = .004) but no longer on day 365 (mean difference, -3.68; -9.30 to 1.94; P = .20). For MADRS-S, the psilocybin group had a significantly greater reduction beginning at day 2 (mean difference, -9.58; 95% CI, -16.05 to -3.11; P = .004), with group differences persisting through day 102 (mean difference, -6.60; 95% CI, -13.01 to -0.19; P = .04) and then isolated effects at days 283 and 343. Most reported treatment-emergent adverse events were transient and of mild to moderate severity. No drug-related serious adverse events were reported. Two participants in the psilocybin group reported persistent, severe anxiety that required medical attention. In this randomized clinical trial of MDD, a single dose of psilocybin was associated with rapid antidepressant effects, observed by day 2 and persisting for more than 3 months on secondary outcomes; psilocybin was generally well tolerated, but some individuals required additional support after dosing due to anxiety. These results suggest that psilocybin may provide a rapid and relatively long-lasting antidepressant effect on major depressive disorder, warranting further investigation into repeated dosing or adjunctive treatment strategies. ClinicalTrials.gov Identifier: NCT04630964.
Clinical relevance
In adults with moderate-to-severe recurrent major depressive disorder (MDD), does a single 25-mg dose of psilocybin combined with psychotherapeutic support produce greater reduction in depressive symptoms than active placebo (niacin 100 mg) at day 8, and does any benefit persist at 6 weeks and 12 months? __SNAPSHOT__ {"studyDesign":"Double-blind, placebo-controlled randomized clinical trial","setting":"Single academic psychiatric clinic (Northern Stockholm Psychiatric Clinic, Karolinska Institutet affiliation), Sweden. Enrollment: January 26, 2021 – February 19, 2024.","sampleSize":"n=35 (psilocybin: n=17; niacin placebo: n=18)","population":"Adults with moderate-to-severe recurrent MDD; mean age 41.0 years (SD 10.1); 60% female. Participants with treatment-resistant depression or cancer-related depression were not the primary target — this trial specifically enrolled the broader MDD population.","intervention":"Single oral dose of psilocybin 25 mg plus 5 structured psychotherapeutic support sessions over 17 days","comparator":"Single oral dose of niacin (nicotinic acid) 100 mg (active placebo) plus 5 structured psychotherapeutic support sessions over 17 days","primaryOutcome":"Between-group difference in change in blinded rater-assessed Montgomery–Åsberg Depression Rating Scale (MADRS) total score from baseline to day 8","followUp":"365 days; secondary clinician-rated MADRS assessments at days 15, 42, and 365; monthly self-report MADRS-S from days 1–365","fundingSource":"Non-profit / government: Norrsken Mind (non-profit) and the Swedish Research Council (grants 2021-01750 and 2021-00462). Funders had no role in study conduct, data analysis, or manuscript preparation. One author (Lundberg) disclosed personal fees from Janssen Cilag unrelated to this work."}
Key findings
The trial met its pre-specified primary endpoint. On day 8, the model-estimated mean between-group difference in MADRS score change was −7.27 points (95% CI, −12.89 to −1.65; P=.01) in favor of psilocybin, indicating a significantly greater reduction in depressive symptoms versus niacin placebo. For context, a MADRS change of 6 is generally considered clinically meaningful and a change of 12 clinically substantial in the literature; the observed primary effect falls within the lower end of the clinically meaningful range. The between-group difference was also statistically significant at the secondary time points of day 15 (mean difference, −11.03; 95% CI, −16.65 to −5.42; P<.001) and day 42 (mean difference, −8.33; 95% CI, −13.94 to −2.71; P=.004), but was no longer statistically significant at day 365 (mean difference, −3.68; 95% CI, −9.30 to 1.94; P=.20). At 6 weeks (day 42), the psilocybin group had a remission rate of 52.9% compared with 5.9% in the niacin group (NNT not calculable from the abstract data alone; absolute risk difference 47.0 percentage points [calculated]). Self-reported MADRS-S showed a significantly greater reduction beginning as early as day 2 (mean difference, −9.58; 95% CI, −16.05 to −3.11; P=.004), with group differences persisting through day 102 (mean difference, −6.60; 95% CI, −13.01 to −0.19; P=.04) and isolated effects at days 283 and 343. Improvements in quality of life and functional disability (secondary outcomes) also persisted for more than 3 months. Regarding safety, the treatment was generally well tolerated with mostly mild-to-moderate transient adverse effects; however, two participants in the psilocybin group experienced severe and persistent anxiety requiring medical attention — a clinically important safety signal given the small sample size (~12% of psilocybin-treated participants [calculated]).
Practice implications
This trial established that a single 25-mg dose of psilocybin with adjunct psychotherapy produced a statistically significant and clinically meaningful reduction in MADRS scores by day 8 in adults with moderate-to-severe recurrent MDD, with benefit sustained through approximately 6 weeks (day 42) and, by self-report, through approximately 3 months. It did NOT establish durable benefit at 12 months by clinician-rated MADRS — the between-group difference at day 365 was non-significant and the confidence interval spanned zero. The trial did NOT include treatment-resistant depression populations, single-episode MDD, patients with active psychosis, or patients on ongoing antidepressants, so findings may not generalize to those groups. Critically, blinding integrity in psilocybin trials is a known and persistent methodological problem — niacin produces flushing but not psychedelic effects, meaning participants could likely identify their allocation, potentially inflating effect sizes through expectancy. This concern is explicitly noted by the authors. The small sample (n=35) limits precision of all estimates, and the single-center design limits generalizability. Participants who remained depressed at day 42 were referred for standard treatment, which may have differentially affected long-term outcomes between groups. Two cases of severe persistent anxiety (~12% of psilocybin-treated participants) underscore that this intervention carries meaningful psychological risk requiring clinical monitoring infrastructure. Practice should NOT change on the basis of this trial alone; rather, these results are encouraging and support the need for larger, multi-site, adequately powered trials with rigorous blinding verification. Only an abstract was available during preparation of this summary; full-text data including baseline characteristics, analytic model specifications, and complete adverse event tables were not independently verified. __LIMITATIONS__ Very small sample size (n=35 total; n=17 psilocybin, n=18 niacin): the trial is substantially underpowered for secondary and subgroup analyses, and all effect estimates carry wide confidence intervals.,Single-center design at a specialized academic psychiatric clinic in Sweden limits generalizability to other clinical settings, healthcare systems, and diverse patient populations.,Active placebo inadequacy and probable functional unblinding: niacin produces a distinctive flushing sensation but no psychedelic experience. Participants in psilocybin trials characteristically identify their allocation at high rates, meaning expectancy effects likely contributed to between-group differences — an acknowledged limitation by the authors themselves.,Loss of between-group separation at day 365 raises important questions about durability of effect and the potential need for repeat dosing; the trial was not designed or powered to resolve this.,Differential post-trial treatment contamination: participants still clinically depressed at day 42 were referred for standard treatment, which could differentially affect long-term outcomes and confound the 12-month comparison.,All secondary MADRS-S data beyond day 42 relied on monthly self-report without clinician verification, introducing self-report bias.,The trial enrolled recurrent moderate-to-severe MDD specifically; findings are not directly applicable to treatment-resistant, first-episode, or psychotic-spectrum presentations.,Absolute effect sizes (e.g., NNT, remission absolute risk differences) and complete adverse event frequency data were not fully extractable from the available abstract.,Statistical significance does not equate to clinical importance: the primary endpoint difference of 7.27 MADRS points, while statistically significant, sits at the lower boundary of what is generally considered clinically meaningful.,Only one author disclosed a potential conflict of interest; however, the broader field of psilocybin research faces inherent enthusiasm bias given investigator and participant expectations. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ In this small (n=35), double-blind, placebo-controlled Swedish RCT, a single 25-mg dose of psilocybin combined with structured psychotherapeutic support produced statistically significant and clinically meaningful reductions in depressive symptoms through 6 weeks in adults with moderate-to-severe recurrent MDD, with self-reported benefit persisting approximately 3 months, but no statistically significant between-group difference at 12 months. Two psilocybin recipients (~12%) developed severe persistent anxiety requiring medical attention, underscoring that this intervention is not risk-free and requires dedicated clinical monitoring infrastructure. These findings are promising and hypothesis-generating but are insufficient to change clinical practice; adequately powered, multi-site trials with rigorous blinding verification are needed before psilocybin therapy can be recommended for routine clinical use in MDD.