The terms empathogen and entactogen are used to designate a class of psychoactive drugs that produce experiences of emotional communion, oneness, relatedness, emotional openness—that is, empathy or sympathy—as particularly observed and reported for experiences with MDMA (ecstasy). This class of drug is distinguished from the classes of hallucinogen or psychedelic, and amphetamine or stimulant. Major members of this class include MDMA, MDA, MDEA, MDOH, MBDB, 6-APB, methylone, mephedrone, aMT, and aET, among others. Most entactogens are phenethylamines and amphetamines, although several, such as aMT and aET, are tryptamines. When referring to MDMA and its counterparts, the term 'MDxx' is often used (with the exception of MDPV). Entactogens are sometimes incorrectly referred to as hallucinogens or stimulants, although many entactogens exhibit psychedelic and/or stimulant properties as well.

Substituted methylenedioxy- phenethylamines (MDxx) are a large chemical class of derivatives of the phenethylamines, which includes many psychoactive drugs that act as entactogens, psychedelics, and/or stimulants, as well as entheogens. These agents are used as research chemicals, designer drugs and as recreational substances.