A web-based survey was used to consult the opinions of experienced drug users on matters related to drug harms. We identified a rare sample of 93 drug users with personal experience with 11 different illicit drugs that are widely used in the UK. Asked to assess the relative harms of these drugs, they ranked alcohol and tobacco as the most harmful, and three "Class A" drugs (MDMA, LSD, and psilocybin) and one class B (cannabis) were ranked as the four least harmful drugs. When asked to assess the relative potential for benefit of the 11 drugs, MDMA, LSD, psilocybin, and cannabis were ranked in the top four; and when asked why these drugs are beneficial, rather than simply report hedonic properties, they referred to potential therapeutic applications (e.g., as tools to assist psychotherapy). These results provide a useful insight into the opinions of experienced drug users on a subject about which they have a rare and intimate knowledge.