While the findings I have discussed in this editorial are both fascinating and promising, I would be remiss if I didn’t invoke a note of caution into all this enthusiasm. It is undeniable that classic psychedelics like psilocybin have profound acute effects on brain function, one does not need a brain scan to see this in the behavioural responses that patients experience during the ‘trips’ that are carefully orchestrated in all the recent studies. But the very obviousness of these effects makes blinding psychedelic treatments difficult in the extreme, at least in terms of patient perception. Moreover, all clinical studies to date of psilocybin have been small, and only two have used a randomized, placebo-controlled design. Many other potential antidepressant treatments that looked promising in the calm waters of small, single-site phase 2 studies floundered out on the wild and wide open seas of large, multi-site phase 3 trials. And while most data to date do not indicate that psychedelics have a high abuse liability, the question remains open as to whether, having tried the medicine once in a study, patients with depression will be at risk for increased future use, whether for recreation or selftreatment.