Portal:Medicine/Selected article/18, 2007
A psychoactive drug or psychotropic substance is a chemical substance that acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and behavior. These drugs may be used recreationally to purposefully alter one's consciousness, as entheogens for ritual or spiritual purposes, or as medication.
Many of these substances (especially the stimulants and depressants) can be habit-forming, causing chemical dependency and may lead to substance abuse. Conversely, others (namely the psychedelics) can help to treat and even cure such addictions. (More...)