A drug is any substance (except for food and water) which, when taken into the body, alters the body’s function either physically and/or psychologically. 

Drugs may be legal (e.g. alcohol, caffeine, tobacco and prescription medication) or illicit (e.g. methamphetamine, cannabis, ecstasy, cocaine and heroin).

The effects of drugs will vary from person to person depending on the person’s characteristics (such as physical size, gender, mood, diet, fitness, age, expectations and health), the drug itself (such as the amount used and its purity), how it is taken, and the environment a person is in when using the drug.