A drug is a substance which may have medicinal, intoxicating, performance enhancing or other effects when taken or put into a human body or the body of another animal and is not considered a food or exclusively a food.
What is considered a drug rather than a food varies between cultures, and distinctions between drugs and foods and between kinds of drug are enshrined in laws which vary between jurisdictions and aim to restrict or prevent drug use. Even within a jurisdiction, however, the status of a substance may be uncertain or contested with respect to both whether it is a drug and how it should be classified if at all. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.
In pharmacology, a drug is "a chemical substance used in the treatment, cure, prevention, or diagnosis of disease or used to otherwise enhance physical or mental well-being." Drugs may be prescribed for a limited duration, or on a regular basis for chronic disorders.
Recreational drugs are chemical substances that affect the central nervous system, such as opioids or hallucinogens. They may be used for perceived beneficial effects on perception, consciousness, personality, and behavior. Some drugs can cause addiction and/or habituation.
Drugs are usually distinguished from endogenous biochemicals by being introduced from outside the organism. 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. Many natural substances, such as beers, wines, and psychoactive mushrooms, blur the line between food and recreational drugs, as when ingested they affect the functioning of both mind and body and some substances normally considered drugs such as DMT (Dimethyltryptamine) are actually produced by the human body in trace amounts.