Research Watch
What “remission” actually meant in the psilocybin depression trials
The largest trial of its kind gave 233 people with treatment-resistant depression a single dose. The three-week result was real. The definition of remission was narrower than it sounds, and the twelve-week figure almost never gets quoted.
When a psychedelic trial reports that patients went into remission, it sounds like a finish line. It is worth knowing what the word is actually measuring, because the answer is narrower than it sounds, and the most interesting number in the whole trial is one that rarely gets quoted.
The trial
In 2022 the New England Journal of Medicine published the largest randomised trial of psilocybin for treatment-resistant depression run to that point. It enrolled 233 adults, all of whom had been through multiple antidepressants without adequate benefit. Each received a single dose alongside psychological support: 79 people at 25mg, 75 at 10mg, and 79 at 1mg, the last acting as the control.
Nobody in the trial was mildly unwell. Average scores on the Montgomery-Asberg Depression Rating Scale, which runs from 0 to 60, sat at 32 or 33 in every group. That is severe territory.
What the numbers showed
Three weeks after the dose, the 25mg group had dropped 12.0 points. The control group dropped 5.4. The difference between them was 6.6 points, with a confidence interval running from 2.9 to 10.2, and it was statistically robust.
The middle dose is the part most coverage skips. The 10mg group dropped 7.9 points, which is only 2.5 points better than control, and that difference could comfortably have been chance. One of the two active doses simply did not beat a control dose that was itself doing something.
What remission actually meant
Remission had a precise, pre-registered definition: a score of 10 or below on that 60-point scale. Response meant a drop of at least half from where you started.
These are useful measures and they are how the whole of psychiatry works. But they describe a position on a questionnaire at a particular moment. They do not mean cured, they do not mean off medication, and they do not mean the depression will not return. Someone can meet the definition of remission and still be someone who has depression.
The number that rarely gets quoted
The trial measured one more thing: sustained response at twelve weeks, meaning people who met the response criteria at week three and held it at every visit after.
The authors put it plainly. Response and remission at three weeks were generally supportive of the primary result. Sustained response at twelve weeks was not.
That single sentence is the most honest thing in the paper, and it is almost never in the headline. A single dose moved severe depression further than a control did, and three weeks later the difference was clear. Twelve weeks later, it was not holding in the way the earlier figures implied.
What it cost
Adverse events affected 179 of the 233 participants, which is 77%. Most were headache, nausea and dizziness. More seriously, suicidal ideation, suicidal behaviour or self-injury occurred in all three dose groups, including the control.
That last detail cuts both ways and deserves care. It is a reminder that this population is seriously unwell to begin with, and also that a single dose of psilocybin did not remove that risk.
Who paid for it
The trial was funded by COMPASS Pathfinder, the company developing the formulation being tested. This is normal in drug development and does not make the results wrong. It does mean the study asking the question had a commercial interest in the answer, which is worth holding in mind whenever a figure from it is quoted at you, including by us.
Where that leaves it
A single dose of psilocybin produced a real, measurable improvement in severe, stubborn depression, larger than a control dose, in the largest trial of its kind. That is a genuinely significant finding and it is why the field has the momentum it has.
It is also a phase 2 trial, in 233 people, with a twelve-week result that did not hold, in a condition people live with for decades. The researchers themselves concluded that larger and longer trials, including comparison with existing treatments, are required.
Both of those things are true at once. Anyone telling you only the first half is selling you something.
Goodwin GM, Aaronson ST, Alvarez O, et al. Single-Dose Psilocybin for a Treatment-Resistant Episode of Major Depression. New England Journal of Medicine, 2022. DOI: 10.1056/NEJMoa2206443
Nothing here is medical advice. Psilocybin is a Class A drug in the UK and these results come from supervised clinical trials with screening, preparation and integration built in, which is not the same as taking mushrooms.
