Sean Carroll in Preposterous Universe:
The Convention on Psychotropic Substances was a 1971 United Nations treaty that placed strong restrictions on the use of psychedelic drugs — not only on personal use, but medical and scientific research as well. Along with restrictions placed by individual nations, it has been very difficult for scientists to study the effects of psychedelics on the brain, despite indications that they might have significant therapeutic potential. But this has gradually been changing, and researchers like Robin Carhart-Harris have begun to perform controlled experiments to see how psychedelics affect the brain, and what positive uses they might have. Robin and I talk about how psychedelics work, how they can help with conditions from addiction to depression, and how they can help people discover things about themselves.
More here.