One Dose, Two Days, One Year: What a Swedish Psilocybin Trial Shows About Depression
Thomas Lee Abshier, ND ·
Why this study is worth a careful look
In May 2026, researchers at the Karolinska Institutet in Stockholm published a randomized, double-blind trial in JAMA Network Open testing a single oral dose of psilocybin, the active compound in so-called magic mushrooms, against an active placebo in adults with recurrent major depression. The headline result is striking: patients who received psilocybin felt better within two days, and on their own ratings the improvement lasted more than three months. The less-publicized result is just as important: by one year, the placebo group had largely caught up.
Both halves of that story deserve attention. Three features set this trial apart from most of the psilocybin literature. First, it enrolled people with ordinary recurrent depression rather than the treatment-resistant or cancer-related depression most earlier trials studied, so it speaks to the much larger population a family physician actually sees. Second, it used an active placebo rather than a sugar pill. Third, it followed every participant for a full year with a control group in place, which few psychedelic trials have done.
The problem it addresses
Major depression is not simply sadness. It is a persistent lowering of mood and loss of interest or pleasure, accompanied by disturbances of sleep, appetite, concentration, energy, and self-regard, severe enough to impair a person’s work and relationships. When episodes come and go over the years, the condition is called recurrent depression.
The standard pharmaceutical answer, the SSRI class of antidepressants, has three well-known limitations. Roughly two-thirds of patients do not reach remission on the first SSRI they try. The drugs typically take several weeks to work, which is a long time for someone who is suffering. And they are often prescribed for years to reduce relapse, during which side effects such as emotional blunting, sexual dysfunction, and weight change make long-term use difficult for many people. A treatment that worked quickly, after one or a few administrations, and did not require daily medication would be a genuine advance, if it held up.
What the researchers did
The trial enrolled 35 Swedish adults, aged 20 to 65 (average age 41; 21 women), with moderate to severe recurrent depression who were in an active episode. None had used psychedelics before, and none were taking antidepressants or receiving psychotherapy when they entered.
Seventeen were randomly assigned to a single 25-mg capsule of psilocybin and eighteen to an identical-looking capsule containing 100 mg of niacin (vitamin B3). We chose niacin because it produces a noticeable flush, in the hope that participants would not easily know which capsule they received. Neither the participants nor the clinicians rating their symptoms were told the assignment.
Every participant, in both groups, also received five psychotherapeutic support sessions over about two and a half weeks: a preparation session, the dosing session itself, and three follow-up sessions. Clinicians administered the dose in a structured, supervised setting.
Clinicians rated depression with the Montgomery-Åsberg Depression Rating Scale (MADRS), a standard 60-point scale, at intervals up to day 365, and patients rated it themselves on a self-report version daily for the first week and periodically thereafter. Participants still depressed at six weeks were referred for standard treatment.
What they found
In the short term, psilocybin clearly outperformed the control. By day 8, the study’s primary endpoint, clinician-rated depression scores had fallen about 7.3 points more in the psilocybin group than in the niacin group, a difference most psychiatrists would regard as clinically meaningful. On self-report, the psilocybin group pulled ahead by day 2 and stayed ahead through day 102.
Remission rates told the same story at six weeks. At day 42, 53% of the psilocybin group were in remission compared with 6% of the niacin group.
By one year, the groups had converged. Remission stood at 53% in the psilocybin group and 41% in the niacin group, a difference small enough to be chance. The pattern underneath is revealing. In the psilocybin group, remission was reached early and then held steady; it did not grow further. In the niacin group, remission rose gradually from 12% to 41% over the year. Similar numbers in each group (6 and 7) began antidepressant medication during that year.
Safety was generally acceptable, with an important exception. Most side effects were temporary: headache, anxiety, and perceptual changes during the session. There were no serious adverse events attributed to the drug. However, two of the seventeen psilocybin patients developed severe anxiety that persisted for weeks after dosing and required medical attention. That is more than one in ten in a small sample, and it should not be passed over.
How to read these results
The sample is very small. With 35 people, we can reliably detect only large effects, and a single unusual participant can move a percentage by six points. The trial was designed to test the eight-day effect, not to settle long-term questions.
The blinding failed. At the end of the study, 94% of the psilocybin group and every niacin participant who answered correctly identified which capsule they received, and most participants also guessed the clinicians’ symptom ratings correctly. Niacin produces a flush; psilocybin produces hours of altered perception. No one confuses them for long. Because depression is measured by interview and self-report, knowing one’s assignment can shape how one reports one’s mood. The participants were recruited through social media and online advertising, which may have drawn people with high hopes for psychedelics, and disappointment can depress scores in a control group just as hope can lift them in a treatment group. This weakness is shared by nearly every psychedelic trial and has no easy solution, but it means the size of the true pharmacological effect remains uncertain.
The one-year convergence has two readings. One reading is that psilocybin did not change the long-term course of the illness; it simply produced a recovery in days that many patients would have reached on their own over months. The other reading is that this is exactly what a good acute treatment should do. Depression is episodic, and many episodes resolve spontaneously; that is why 41% of the niacin group were in remission by a year. A treatment that moves the recovery forward by months spares a person months of suffering, lost work and strained relationships, even if it does not change where he ends up. Both readings are consistent with the data. The data do not show that a single dose prevents future episodes, and that was one of the main hopes for psilocybin.
The setting was part of the treatment. Both groups received five sessions of psychological support. The results describe psilocybin given in a screened, supervised, therapeutic context, not psilocybin in general. The trial cannot tell us how much of the benefit came from the drug, how much from the drug interacting with the support, and how much from the support alone.
A lesson that applies to every therapy. The niacin group’s steady climb to 41% remission is a reminder that applies equally to natural and conventional treatments: depression often improves with time, so any remedy taken during an episode will appear to work for a good share of the people who take it. Only a controlled comparison separates the remedy from the illness’s natural course. This trial is valuable partly because it had a control group and kept it for a full year.
What may be going on physiologically
The body converts psilocybin to psilocin, which acts chiefly on the serotonin 5-HT2A receptor. A leading hypothesis is that this triggers a window of increased neuroplasticity, growth and reorganization of connections between neurons, during which entrenched patterns of thought and brain-network activity become more flexible. The investigators note that depression appears to involve impaired communication between brain regions, possibly linked to synaptic changes, and the trial’s registry entry indicates they also set out to measure synaptic density. Those results are not part of this paper. The plasticity hypothesis is plausible and supported by animal work, but in humans it remains a working model rather than an established mechanism.
Practical guidance for readers
This is not a reason to self-treat. The trial used a pharmaceutical-grade, precisely measured dose in carefully screened patients, with supervision, preparation, and follow-up. Wild or home-grown mushrooms vary widely in potency, and the two persistent anxiety reactions occurred even under the best conditions.
Some people should not take psilocybin at all. Clinical trials routinely exclude anyone with a personal or family history of psychosis or bipolar disorder, because psychedelics can precipitate psychotic or manic episodes. People taking lithium face a reported risk of seizures in combination with psychedelics. Anyone on an antidepressant should not stop it abruptly in order to try something else; discontinuation should be planned with the prescribing clinician.
The legal situation is changing, but it hasn’t changed yet. Psilocybin remains a Schedule I controlled substance under federal law. Oregon and Colorado operate licensed state programs, and New Mexico has enacted a medical psilocybin law whose program is targeted to begin by the end of 2026. Compass Pathways expects to complete its application to the FDA for a synthetic psilocybin treatment for treatment-resistant depression in the fourth quarter of 2026, and the Usona Institute is developing psilocybin for major depressive disorder. Outside those state programs and approved clinical trials, possession is illegal. Readers interested in participating in research can search for open psilocybin studies at clinicaltrials.gov.
Conclusion
This is a small but well-constructed trial with a real signal. A single supervised dose of psilocybin, combined with brief psychological support, produced rapid and clinically meaningful relief in people with ordinary recurrent depression, relief that appeared within days and lasted for months. On this evidence, it did not change the one-year outcome, and the failure to blind means the true effect size is still unknown. The honest conclusion is the one the authors drew: the findings justify larger trials, including trials of repeated dosing and of psilocybin added to other treatments, before anyone can say what place it should have in the care of depression.
If you or someone you know is in crisis, call or text 988 (the Suicide and Crisis Lifeline in the United States).
Reference
Yngwe H, Plavén-Sigray P, Ekman CJ, Henje E, Berglund A, Tiger M, Beckman M, Lundberg J. Short-Term and Late-Term Effects of Psilocybin on Symptoms in Major Depression: A Randomized Clinical Trial. JAMA Network Open. 2026;9(5):e2612589. doi:10.1001/jamanetworkopen.2026.12589