A drug is any chemical substance that has an effect on the body. Drugs can be used for therapeutic purposes to treat diseases or medical conditions, or they can be used recreationally to alter mood or consciousness. Drugs can be derived from natural sources such as plants or animals, or they can be synthesized in a laboratory. They can be administered in various ways, including orally, intravenously, or topically. The effects of drugs on the body can vary widely depending on the specific drug and the individual's physiology.