Originally Posted by tennis_badger
fed is the least likely to dope/take any drugs.
nadal is suspicious, murray and joker i think is clean as well like fed.
unlike bike racing and baseball, tennis is not an endurance sport or one that requires hitting the ball really hard, so i dont think dope is that effective (very min knowledge about dope, so maybe i'm wrong)
one thing that lance did was to re-inject his fresh blood to keep him fresh, this is more possible scenario in tennis, however considering the amount of tournaments they played and in different countries i dont see this happening (storing and moving blood package undetected year after year? yeah i dont think so) and even if it happen it'll be on occassion where the person is really tired, wont be on every match, maybe before a GS final or something.
When you play 4-5 hours, and then have to play the next day endurance can certainly help. Drugs can make players run faster and extra strength will help hit the ball harder. Some drugs can even improve hand-eye coordination... think of Barry Bonds. And other drugs can help a player calm his/her nerves.