This study used a web-based questionnaire to investigate user perceptions of the benefits and harms of hallucinogenic drug use. Over 600 forms were submitted. Users were asked to comment on the acute and prolonged effects of different drugs and to provide more specific information on how par- ticular drugs have harmed and/or helped them. Subjects reported relatively less harm associated with the classic hallucinogens, LSD and psilocybin, than other drugs specifically focused on in the ques- tionnaire (MDMA, cannabis, ketamine and alcohol). A wide-range of benefits was reported, includ- ing: help with mood disorders, addictions and migraine as well as more general long-term improvements in wellbeing. Symptoms of hallucinogen persisting perceptual disorder were reported by a number of subjects and these were most closely associated with use of LSD; however, few users regarded these effects as troubling. Eighty-one per cent of users reported having had a ‘spiritual experience’ on a hallucinogenic drug and over 90% considered ‘access to the unconscious mind’ to be a specific property of the classic hallucinogens. With caution, these findings support recent calls for a systematic investigation of the therapeutic potential of the classic hallucinogens and highlight the scope for empirical investigations of spiritual and psychodynamic phenomena. Keywords: Hallucinogens, psychedelics, LSD, psilocybin.