Psychoactive Drug

A psychoactive drug (or psychotropic drug) is a chemical substance that changes the function of the nervous system and results in alterations of perception, mood, cognition, and behavior. These substances may be used medically, recreationally, for spiritual reasons (for example, by altering one's consciousness, as with entheogens for ritual, spiritual, or shamanic purposes), or for research. Some categories of psychoactive drugs may be prescribed by physicians and other healthcare practitioners because of their therapeutic value.

Broadly speaking, psychoactive drugs fall into one of four primary classifications – stimulants, depressants, antipsychotics and hallucinogens, although there can be some overlap in effects, making some difficult to relegate to a single category. The psychedelics are a subclass of the hallucinogens category.