Novel synthetic ‘designer’ drugs with stimulant, ecstasy-like (entactogenic) and/or hallucinogenic properties have become increasingly popular among recreational drug users in recent years. In this article, the authors review the available information on this group of drugs, and provide a framework for their classification based on chemical structure, and describe their pharmacology and clinical toxicology. Overall, the authors conclude that “there are limited reliable data to guide clinicians managing patients with toxicity due to these substances. The harms associated with emerging recreational drugs are not fully documented, although it is clear that they are not without risk. Management of users with acute toxic effects is pragmatic and primarily extrapolated from experience with longer established stimulant or hallucinogenic drugs such as amphetamines, MDMA and LSD.