Define drug and drug abuse.

Pharmacologically, a drug is any substance that chemically alters the function or structure of a living organism. This definition would include food, insecticides, air pollutants, water pollutants, acids, vitamins, toxic chemicals, soaps, and soft drinks.

In medicine, a drug is any substance that is manufactured specifically to relieve pain or to treat or prevent diseases and other medical conditions.

In a social problems approach, a drug is any habit-forming substance that directly affects the brain and the nervous system. It is a chemical that affects moods, perceptions, body functions, or consciousness, and that has the potential for misuse because it may be harmful to the user.

Drug abuse is the regular or excessive use of a drug when, as defined by a group, the consequences endanger relationships with other people, are detrimental to the user's health, or jeopardize society itself. This definition identifies two key factors that determine what is considered drug abuse in a society: The first is the actual drug effects, and the second is a group's perception of the effects.