Psychoactive Drug

A substance capable of altering attention, memory, judgment, time sense, self-control, mood, or perception.

Definition from Coon and Mitterer's Psychology: Modules for Active Learning, (2009, p. 229)

Psychoactive drugs are a class of chemical substances that act on the central nervous system and can alter behavior and cognition. All psychoactive drugs are highly fat-soluble and thus cross the blood-brain barrier readily. Psychoactive drugs alter synaptic transmission by altering neuro-transmitter amounts and availability or by affecting receptor activity. In addition to the drug's primary effects on behaviors such as arousal, thought processes, mood, perception, and consciousness, psychoactive drugs can produce a variety of nonbehavioral effects that may more directly affect health and, in some instances, can lead to death.

Although there are several different classification schemes for psychoactive drugs (pharmacological, legal, medical), the most common organization is based on their effect on behavior and cognition. According to this scheme, psychoactive drugs can be classified into four broad categories: (1) sedatives and hypnotics, (2) stimulants, (3) opiates, and (4) hallucinogens and psychedelics.

Excerpt from Psychoactive Drugs

For a larger helpful image of the drug categories and the drugs in each category (slightly different from those named above), see Psychoactive Drug Venn Diagram

Psychoactive Drugs Venn Diagram.jpg