Athletes use drugs for many reasons. Some use drugs for medical need. Some use proscribed drugs inadvertently, while others use drugs deliberately - either on their own initiative or at the behest of coaches or officials - to cheat, to try to improve their performance artificially and to improve their chances of winning. Finally, some sports people use drugs, including illegal drugs, recreationally.
Baume, P. (1994). Drugs in sport. Australian Prescriber, retrieved 01/10/2015.