Drug is, in the broadest of terms, a chemical substance that has
known biological effects on humans or other animals. Foods are generally
excluded from this definition, in spite of their physiological effects on
animal species.
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. Pharmaceutical drugs may be used 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. Alcohol, nicotine, and caffeine are the most widely consumed
psychotropic drugs worldwide.
They may be used for effects on
perception, consciousness, personality, and behavior. Many recreational drugs
are also medicinal.
Some drugs can cause addiction and
habituation and all drugs
have side effects. Many drugs are illegal for recreational purposes and
international treaties such as the Single Convention on Narcotic Drugs exist
for the purpose of legally prohibiting certain substances.
