A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function[5]. There is no single, precise definition, as there are different meanings in medicine, government regulations, and colloquial usage.[6]

In pharmacology, Dictionary.com defines a drug as “a chemical substance used in the treatment, cure, prevention, or diagnosis of disease or used to otherwise enhance physical or mental well-being.”[6] Drugs may be prescribed for a limited duration, or on a regular basis for chronic disorders.[7]

Recreational drugs are chemical substances that affect the central nervous system, such as narcotics or hallucinogens.[7] They may be used for perceived beneficial effects on perception, consciousness, personality, and behavior.[7][8] Some recreational drugs can cause addiction and habituation.[8]

Drugs are usually distinguished from endogenous biochemicals by being introduced from outside the organism.[citation needed] For example, insulin is a hormone that is synthesized in the body; it is called a hormone when it is synthesized by the pancreas inside the body, but if it is introduced into the body from outside, it is called a drug.[citation needed]

Many natural substances such as beers, wines, and some mushrooms, blur the line between food and drugs, as when ingested they affect the functioning of both mind and body.