A caffeine molecule. Caffeine is a common drug

According to the WHO, a drug is a substance that can change how a living organism works. Food is usually not seen as a drug, even though some foods may have such properties. Most of the time drugs are taken to treat a disease, or other medical condition. An example for such drugs may be Aspirin or Paracetamol. These are usually given to treat fever, as well as certain infections. If such drugs are taken over a longer time, they are usually prescribed by a doctor. Other drugs are taken for fun, because of the effect they have. Some of these drugs taken for fun are better accepted by society than others. Having or taking certain drugs may be illegal, in certain countries.