Updated June 23, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Definition: Homeostasis is the process by which the body attempts to maintain a state of stable physiological balance, even in a changing environment. For instance, in a cold environment, warm-blooded animals (like us) constrict their cutaneous blood vessels and begin shivering, in order to maintain their internal body temperature.

The body needs to maintain homeostasis in order to stay alive. If you take a psychoactive drug, your body may attempt to bring itself back into this physiologic balance, and this may create a rebound effect.

Pronunciation: hO-mee-O-stay-sis

Example: If you take a drug sedative drug, the body may attempt to maintain homeostasis resulting in agitation.

Edited by Richard N. Fogoros, MD