Psychoactive drug

A psychoactive drug, psychopharmaceutical, mind-altering drug, consciousness-altering drug, psychoactive substance, or psychotropic substance is a chemical substance that alters psychological functioning by modulating central nervous system (CNS) activity. Psychoactive and psychotropic drugs both affect the brain, with psychotropics sometimes referring to psychiatric drugs or high-abuse substances, while “drug” can have negative connotations. Novel psychoactive substances are designer drugs made to mimic illegal ones and bypass laws.

Psychoactive drug use dates back to prehistory for medicinal and consciousness-altering purposes, with evidence of widespread cultural use. Many animals intentionally consume psychoactive substances, and some traditional legends suggest animals first introduced humans to their use. Psychoactive substances are used across cultures for purposes ranging from medicinal and therapeutic treatment of mental disorders and pain, to performance enhancement. Their effects are influenced by the drug itself, the environment, and individual factors. Psychoactive drugs are categorized by their pharmacological effects into types such as anxiolytics (reduce anxiety), empathogen–entactogens (enhance empathy), stimulants (increase CNS activity), depressants (decrease CNS activity), and hallucinogens (alter perception and emotions). Psychoactive drugs are administered through various routes—including oral ingestion, injection, rectal use, and inhalation—with the method and efficiency differing by drug.

Psychoactive drugs alter brain function by interacting with neurotransmitter systems—either enhancing or inhibiting activity—which can affect mood, perception, cognition, behavior, and potentially lead to dependence or long-term neural adaptations such as sensitization or tolerance. Addiction and dependence involve psychological and physical reliance on psychoactive substances, with treatments ranging from psychotherapy and medication to emerging psychedelic therapies; global prevalence is highest for alcohol, cannabis, and opioid use disorders.

The legality of psychoactive drugs has long been controversial, shaped by international treaties like the 1961 Single Convention on Narcotic Drugs and national laws such as the United States Controlled Substances Act. Distinctions are made between recreational and medical use. Enforcement varies across countries. While the 20th century saw global criminalization, recent shifts favor harm reduction and regulation over prohibition. Widely used psychoactive drugs include legal substances like caffeine, alcohol, and nicotine; prescribed medications such as SSRIs, opioids, and benzodiazepines; and illegal recreational drugs like cocaine, LSD, and MDMA.

Psychoactive drug use can be traced to prehistory. Archaeological evidence of the use of psychoactive substances, mostly plants, dates back at least 10,000 years; historical evidence indicates cultural use 5,000 years ago. There is evidence of the chewing of coca leaves, for example, in Peruvian society 8,000 years ago.

Psychoactive substances have been used medicinally and to alter consciousness. Consciousness altering may be a primary drive, akin to the need to satiate thirst, hunger, or sexual desire. This may be manifest in the long history of drug use, and even in children's desire for spinning, swinging, or sliding, suggesting that the drive to alter one's state of mind is universal.

In The Hasheesh Eater (1857), American author Fitz Hugh Ludlow was one of the first to describe in modern terms the desire to change one's consciousness through drug use:

[D]rugs are able to bring humans into the neighborhood of divine experience and can thus carry us up from our personal fate and the everyday circumstances of our life into a higher form of reality. It is, however, necessary to understand precisely what is meant by the use of drugs. We do not mean the purely physical craving ... That of which we speak is something much higher, namely the knowledge of the possibility of the soul to enter into a lighter being, and to catch a glimpse of deeper insights and more magnificent visions of the beauty, truth, and the divine than we are normally able to spy through the cracks in our prison cell. But there are not many drugs which have the power of stilling such craving. The entire catalog, at least to the extent that research has thus far written it, may include only opium, hashish, and in rarer cases alcohol, which has enlightening effects only upon very particular characters.