I'm not sure (you can look it up as well as anyone), but from what I've heard (again, Pollan's book), controlled, randomized trials are very difficult if not impossible with psychedelics. It's obvious to both the patient and the observer who has received a placebo and who has not. That's part of the problem with studying this class of drugs, what we have considered the gold standard for clinical trials isn't effective here. So do we trust what results we do see or dismiss them because of their nature?
When a small study shows that 80% of smokers stop cold-turkey after a single session and 60% of them are still abstinent a year later (versus 30% for therapy), it's hard to discount the results so long as other trusted methods are used.
N = 15. I understand that there are a lot of regulatory obstacles to performing large-scale clinical trials into psychedelics, but the overall quality of the research so far is indifferent. A great number of ineffective and mediocre interventions have been made to look miraculous by a handful of small open-label trials. The homeopathy community has produced a mountain of similar trials.
Psychedelics do indeed look promising and have a plausible mechanism for providing very large effect sizes, but it really is too early to draw any firm conclusions. The authors have registered a larger comparative efficacy trial, so I look forward to seeing their results if and when they are published.
Can you even judge the sample size separate from effect size?
If 15 out of 15 people register an improvement it's a lot more meaningful than 3 out of a 100 sample, despite the much larger sample size in the latter case.
There is one psilocybin study by Compass Pathways starting this year in 8 EU countries with I think about 800 participants which if successful will pave the way for legal use of psilocybin therapy of depression. MAPS is doing another one for MDMA for PTSD, that's FDA Phase 3 in 14 international sites.
When a small study shows that 80% of smokers stop cold-turkey after a single session and 60% of them are still abstinent a year later (versus 30% for therapy), it's hard to discount the results so long as other trusted methods are used.
Study using psilocybin for smoking cessation: https://www.ncbi.nlm.nih.gov/pubmed/27441452 Study using CBT for smoking cessation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4119230/