A psychoactive substance is a chemical substance—other than a nutrient or essential dietary ingredient—that alters brain function to produce temporary changes in sensation, perception, mood, consciousness, cognition, and behavior.
Psychoactive substances have been used by humans for a variety of purposes since recorded history. For example, they can be taken recreationally for their pleasurable or euphoric effects and novelty value, as entheogens for ritual or spiritual purposes, or as scientific research tools for studying the brain and mind. The latter two have particular relevance for practitioners of psychonautics. Many psychoactive substances have established therapeutic utility and are used in routine medical practice (e.g. anaesthetics, analgesics, anxiolytics, antidepressants, etc.).
The Psychoactive Substance Index (PSI) is designed to catalog and provide relevant, accurate, and unbiased information for any and all psychoactive substances, with special attention given to those that have utility as mind-expanding tools. The individual articles detail not just the history, chemistry, pharmacology, toxicity, and legality of each substance, but also their unique profile of subjective effects (phenomenology). This is done in accordance with a standardized system of definitions and terminologies found in the Subjective Effect Index (SEI).
Please see our summary index to view conveniently condensed versions of each article.