While hallucinogens have a long record of culturally sanctioned and salutary use, dating back thousands of years to pre-historical indigenous communities, their emergence since the 1960s as recreational drugs have led to maladaptive patterns of use and risks to young people. Adverse outcomes can include high levels of acute anxiety, psychotic decompensation that usually though not always resolves, and a chronic disabling condition identified as hallucinogen persisting perception disorder (HPPD). Over the past twenty years additional concerns have been aroused by use of MDMA (aka Ecstasy), which has achieved high levels of popularity among young people as a recreational dance drug. Other new trends among youth include experimentation with the dissociative hallucinogens, ketamine and salvia divinorum. With the re-emergence of approved and methodologically sound clinical investigations of hallucinogens, a better understanding of the full range of effects these highly unusual compounds have will evolve.