In pharmacy, a drug or pharmaceutical is a substance used to prevent, cure, or alleviate the symptoms of a disease or ailment. Drugs can be taken orally, via a skin patch, by injection, or via an inhaler, among other methods. Some drugs are available over-the-counter, while others require a prescription from a doctor. The pharmaceutical industry is responsible for the development and marketing of drugs, and it is a key component of the health sector, which is the most profitable industry in the U.S. economy.

Pharmaceutical drugs may be used for a limited duration or on a regular basis for chronic disorders. They are often classified into drug classes, which are groups of related drugs that have similar chemical structures, the same mechanism of action, and are used to treat the same disease.

Drugs can also refer to illegal or restricted substances used recreationally or to get high.

Pharmacology is the study of drugs and their effects on the body. Pharmacokinetics is a subfield of pharmacology that studies what happens to drugs once they enter the body, including absorption, distribution, metabolism, and excretion.

In summary, a drug in pharmacy is a substance used to prevent, cure, or alleviate the symptoms of a disease or ailment. It can be taken in various ways and may require a prescription. The pharmaceutical industry is responsible for the development and marketing of drugs, and pharmacology is the study of drugs and their effects on the body.