I don't know if using performance enchancing drugs is covered on tournament rules but right now there is no check up before games so a player who plays "doped" will not be caught unless he openly admits it.

Since there is a perceived boost in performance  and no punishment in doing it I won't be surprised if lots of players use it.

By lots I mean basically everybody with perhaps the exception of people who aren't positively affected by it. Specially on big events with big prizes.

Did I mentioned The International reached a 16 million prize poll?