Drugs may be classified in a variety of ways The most common method is to group drugs according to their general purpose or use. For example, drugs are often categorised into those used to fight disease and those used to relieve pain. Alternatively, drugs may be classified according to the way they are administered to a patient. For instance, they may be grouped into those taken orally, those injected into the body, those applied to the body surface and those inserted into a body opening. Drugs may also be categorised according to their form: tablet, liquid, ointment or powder