David Jay Brown in Scientific American:
Current studies are focusing on psychedelic treatments for cluster headaches, depression, obsessive-compulsive disorder (OCD), severe anxiety in terminal cancer patients, post-traumatic stress disorder (PTSD), alcoholism and opiate addiction. New drugs must pass three clinical milestones before they can be marketed to the public, called phase I (for safety, usually in 20 to 80 volunteers), phase II (for efficacy, in several hundred subjects) and phase III (more extensive data on safety and efficacy come from testing the drug in up to several thousand people). All the studies discussed in this article have received government approval, and their investigators are either in the process of recruiting human subjects or have begun or completed research on human subjects in the first or second stage of this trial process.
Psychedelic drugs affect all mental functions: perception, emotion, cognition, body awareness and one’s sense of self. Unlike every other class of drugs, psychedelic drug effects depend heavily on the environment and on the expectations of the subject, which is why combining them with psychotherapy is so vital.
“Psychedelics may be therapeutic to the extent that they elicit processes that are known to be useful in a therapeutic context: transference reactions and working through them; enhanced symbolism and imagery; increased suggestibility; increased contact between emotions and ideations; controlled regression; et cetera,” says psychiatrist Rick Strassman of the University of New Mexico School of Medicine, who from 1990 to 1995 performed the first human study using psychedelic drugs in about 20 years, investigating the effects of DMT on 60 human subjects.