A psychoactive drug or psychotropic substance is a chemical that acts primarily upon the central nervous system, but also to a lesser extent upon the autonomic nervous system and the peripheral nervous system. This alteration of brain function can result in temporary changes in perception, mood, consciousness and behavior.
These drugs may be used recreationally to purposefully alter one's consciousness (such as coffee, alcohol or cannabis), as entheogens for spiritual purposes (such as the mescaline containing peyote cactus or psilocybin containing mushrooms), and also as medication (such as the use of narcotics in controlling pain, stimulants to treat narcolepsy and attention disorders, as well as anti-depressants and anti-psychotics for treating neurological and psychiatric illnesses).
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.
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Council on Spiritual Practices - Readings on religious experience, spiritual practices and traditions, and the use of psychoactive drugs to stimulate or enhance religious experience.
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