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.
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/