A psychoactive drug, psychopharmaceutical, or psychotropic drug is a chemical substance that changes nervous system function and results in alterations in perception, mood, consciousness, cognition, or behavior. These substances may be used medically; recreationally; to purposefully improve performance or alter one's consciousness; as entheogens for ritual, spiritual, or shamanic purposes; or for research. Some categories of psychoactive drugs, which have therapeutic value, are prescribed by physicians and other healthcare practitioners. Examples include anesthetics, analgesics, anticonvulsant and antiparkinsonian drugs as well as medications used to treat neuropsychiatric disorders, such as antidepressants, anxiolytics, antipsychotics, and stimulant medications. Some psychoactive substances may be used in the detoxification and rehabilitation programs for persons dependent on or addicted to other psychoactive drugs.
Psychoactive substances often bring about subjective (although these may be objectively observed) changes in consciousness and mood that the user may find rewarding and pleasant (e.g., euphoria or a sense of relaxation) or advantageous in an objectively observable or measurable way (e.g. increased alertness). Substances which are rewarding and thus positively reinforcing have the potential to induce a state of addiction – compulsive drug use despite negative consequences. In addition, sustained use of some substances may produce physical or psychological dependence or both, associated with somatic or psychological-emotional withdrawal states respectively. Drug rehabilitation attempts to reduce addiction, through a combination of psychotherapy, support groups, and other psychoactive substances. Conversely, certain psychoactive drugs may be so unpleasant that the person will never use the substance again. This is especially true of certain deliriants (e.g. Jimson weed), powerful dissociatives (e.g. Salvia divinorum), and classic psychedelics (e.g. LSD, psilocybin), in the form of a "bad trip".
Psychoactive drug misuse, dependence and addiction have resulted in legal measures and moral debate. Governmental controls on manufacture, supply and prescription attempt to reduce problematic medical drug use. Ethical concerns have also been raised about over-use of these drugs clinically, and about their marketing by manufacturers. Popular campaigns to decriminalize or legalize certain recreational drug use (e.g. cannabis) are also ongoing.