Re: psychedelics & psychosis risk, see Krebs & Johansen 2013, a study of National Survey on Drug Use and Health data (n = 130,152) which found:
21,967 respondents (13.4% weighted) reported lifetime psychedelic use. There were no significant associations between lifetime use of any psychedelics, lifetime use of specific psychedelics (LSD, psilocybin, mescaline, peyote), or past year use of LSD and increased rate of any of the mental health outcomes.
Rather, in several cases psychedelic use was associated with lower rate of mental health problems.
Unfortunately, it’s not a randomized, forward-looking trial. I personally give high-quality retrospective survey research like this some weight when thinking through the risks associated with psychedelics. (And more research is needed, as always.)
See also Krebs & Johansen 2015 for similar results with a different data set:
Using a new data set consisting of 135,095 randomly selected United States adults, including 19,299 psychedelic users, we examine the associations between psychedelic use and mental health. After adjusting for sociodemographics, other drug use and childhood depression, we found no significant associations between lifetime use of psychedelics and increased likelihood of past year serious psychological distress, mental health treatment, suicidal thoughts, suicidal plans and suicide attempt, depression and anxiety. We failed to find evidence that psychedelic use is an independent risk factor for mental health problems.