At the same time the way the ATP schedules the season and awards points almost forces most players (ranked 20 and lower?) to play as much as possible in order to eek out a good wage. Unlike in baseball where illegal drugs serve only as performance enhancers (let's admit that baseball is not the most physically grueling sport even for the pitcher), in professional tennis it could almost be defended as being a necessity in some instances. It's almost like a trucking company telling it's drivers they HAVE to span so many miles in so many hours or else they're fired, but they can't ingest caffeine.
But Fed has a point. They should know. I'm sure there's a lot more doping and drug taking than we know about. I mean, winning the French Open must take a level of fitness rarely required in all of sports. The temptation to take drugs or to dope the blood must be high when you've just played two five setters in a row on red clay and you have tons of points to defend, and bills to pay. Just saying.