Why do athletes use illegal drugs?

Actor Robin Williams once famously remarked: "A cocaine addiction is God's way of telling you that you are making too much money". In the case of athletes, he could have added:"...and that you have too much free time in which you don't know what to do with yourself". In the case of marijuana, athletes are mostly doing what millions of people their age are doing. Marijuana is also known for making its users unwind mentally, which may be not altogether a bad thing for professional athletes who have to wind themselves up continually in order to be competitive.