Very few long-term studies of psilocybin for depression have been conducted to date, said Dr. Charles Raison, a professor of human ecology and psychiatry at the University of Wisconsin-Madison who was not involved in the research.
“They are very difficult to do because people drop out,” Raison told Live Science in an email. “But also because they go on all sorts of other treatments that obfuscate the degree to which any longer lasting benefits result from the psychedelic or because the participant got therapy or restarted an antidepressant.”