A 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.