Medicines and drugs Drugs of abuse 1. A drug is a chemical substance which affects how parts of the body work. The drug might affect one organ such as the heart, or a full body system such as the nervous system. All medicines are drugs, but they are legal substances which have been carefully developed and tested to make sure they are safe to use. Many medicines are only available with a doctor's prescription and all of them should be taken in measured doses.
Drugs of abuse are substances which are harmful to the body.
Unlike medicines, they have not been tested to make sure they are safe. Drugs of abuse are often illegal and some are extremely dangerous. Some drugs cause damage, for example to the brain or the liver. Many drugs are addictive and so the user can't give them up easily. The problems facing smokers Caffeine and alcohol can be misused, though in small amounts they are not thought to cause health problems.