A psychoactive substance is a chemical substance that crosses the blood-brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior. These substant may be used recreationally, to purposefully alter one's consciousness, as entheogens for ritual or spiritual purposes, as a tool for studying or augmenting the mind, or therapeutically as medication.
Because psychoactive substances bring about subjective changes in consciousness and mood that the user may find pleasant (e.g. euphoria) or advantageous (e.g. increased alertness). Many psychoactive substances are abused, that is, used excessively, despite risks or negative consequences. With sustained use of some substances, physical dependence may develop, making the cycle of abuse even more difficult to interrupt. Drug rehabilitation aims to break this cycle of dependency, through a combination of psychotherapy, support groups and even other psychoactive substances.
In part because of this potential for abuse and dependency, the ethics of the substance use are the subject of a continuing philosophical debate. Many governments worldwide have placed restrictions on drug production using these substance and sales in an attempt to decrease drug abuse.
Psychoactive drugs are divided into 3 groups:
1. Depressants - those that slow down the central nervous system; such as tranquilizers, alcohol, heroin and other opiates, cannabis (in low doses)
2. Stimulants- those that excite the nervous system; such as nicotine, amphetamines, cocaine, caffeine, chocolate
3. Hallucinogens - those that alter how reality is perceived; such as LSD, mescaline, Psilocybin mushrooms, Salvia divinorum.
Caffein and Chocolate the world's most widely consumed psychoactive substance, but unlike many others, it is legal and unregulated in nearly all jurisdictions. In North America, 90% of adults consume caffeine daily.
src: WIKIPEDIA.COM
