Generally speaking, a drug is a substance which when ingested, smoked, injected, or absorbed into the body by any other method, causes either a mental and/or physical change within the organism. It is different from food in that it is not consumed primarily for the purpose of nourishment. When taken to promote health, or to combat a disease or an infection, it is generally referred to as a "medical" drug. Any other use is generally thought of as "recreational". The drugs described in this article fall into this final category.