D Introduction Methylenedioxymethamphetamine (MDMA), Ketamine, Gamma Hydroxybutyrate (GHB), and Rohypnol are unique compounds, differing in terms of their pharmacological properties and their phenomenological effects. The common thread linking these disparate drugs is the people who use them. These substances are used throughout the world most frequently by a sophisticated, adolescent or twenty-something constituency, as well as within the gay subculture. The drugs are widely used and abused at urban social gatherings both in commercial and informal settings. They are most commonly used in nightclubs and all-night dance marathon parties known as "raves" and at gay "circuit parties." Composed primarily of affluent gay men, "circuit parties" are large social gatherings held in many different countries, usually on weekends and holidays. These drugs, which will be discussed extensively, and several others, which will be described more briefly, are widely known as "club drugs."