A May 2026 trial from Karolinska Institutet gave 35 people with depression a single dose of psilocybin or an active placebo, then kept following them for a full year — the most rigorous long-term test yet of the “one dose, lasting relief” story. The honest answer it found: yes, dramatically, for a while — and then the picture gets more complicated.
Most psilocybin depression trials share a structural weakness: they follow people for a matter of weeks, sometimes a couple of months, then stop — right around the point where a fair test of “does this really last” would just be getting started. A team at Sweden’s Karolinska Institutet, led by Hampus Yngwe and Johan Lundberg, built a trial specifically to close that gap: a double-blind, placebo-controlled study that followed participants for a full twelve months, published in JAMA Network Open on May 15, 2026.
A genuinely rigorous design
Thirty-five adults with recurrent major depressive disorder were randomized, roughly evenly, to a single 25 mg dose of psilocybin or a single 100 mg dose of niacin — chosen specifically as an “active placebo” because it causes a flushing sensation that can mimic some of the bodily feeling of a psychedelic session, an attempt to make the blinding more honest than an inert sugar pill would allow. Both groups received identical psychological support: five structured sessions across seventeen days, including preparation, the dosing day itself with seven hours of supervised observation, and three follow-up integration sessions.
Fast, real, and — for a while — durable
The results, on their own terms, were striking. The trial’s primary outcome — the change in clinician-rated depression scores by day 8 — showed a statistically significant 7.27-point advantage for psilocybin over niacin. That advantage didn’t fade quickly, either: it peaked around day 15, remained significant through day 42, with more than half of the psilocybin group (52.9%) in remission at six weeks compared to just 5.9% of the niacin group. Participants’ own self-reported ratings showed benefits detectable as early as day 2 and still measurable, in a more limited form, past the three-month mark.
Where the story gets genuinely more complicated
Here’s where this trial earns its place as more than another positive headline. By day 365, the clinician-rated advantage over placebo had disappeared entirely — not because the psilocybin group got worse, but because the niacin group kept improving on its own, with remission rates in that group climbing from under 12% early on to 41.2% by the one-year mark. Some of that is very likely ordinary spontaneous recovery, the kind depression often shows regardless of treatment; the psychological support both groups received throughout may have played a real role too. Either way, the study’s own authors were direct about what this means: whatever benefit a single dose of psilocybin provides may need a booster dose or ongoing maintenance therapy to keep from fading — a real complication for anyone hoping “one session, done” would be the eventual clinical reality.
The study is equally candid about a second, more methodological problem that runs through nearly every psychedelic trial ever conducted: blinding essentially didn’t work. Ninety-four percent of the psilocybin group correctly guessed which arm of the trial they’d been assigned to, and every single niacin participant guessed correctly too — hardly surprising, given how obviously different an actual psychedelic experience feels from a niacin flush, but a real problem for isolating how much of the measured benefit came from the drug’s pharmacology versus simply knowing, quite confidently, that you’d received it. The authors don’t paper over this: they call it out explicitly as a limitation any future trial in this space will need to solve.
Safety, briefly
The drug was generally well tolerated — most adverse events (headache, transient anxiety, the expected perceptual effects) were mild to moderate and resolved on their own, and no serious adverse event was judged related to the psilocybin itself. Two participants did experience severe, persisting anxiety that required medical attention in the weeks following their session, a reminder — echoed across nearly every serious trial this site has covered — that these sessions aren’t universally benign even under careful clinical supervision.
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