I highly doubt most of the elite fighters are doing PEDs. The main reason is the GSP's, Cain's and Silva's of the MMA have way way too much to lose if they are caught using PEDs.
Look no further than Sean Sherk. People might forget but until late July 2007 it looked like Sherk was going to do go down as a Hall of Famer. The guy had two one sided LW wins and win over Nick Diaz (who knocked off Gomi) so for a few weeks Sherk was the number 1 ranked LW in the world. He was set to face BJ Penn in what was going to be the biggest LW fight in history and no matter what the outcome cement his legacy in the UFC. He failed his drug test and is now pretty much a forgotten champion. That can happen to anyone with one failed drug test and you bet GSP or Cain or Silva know that. So the risk is too much for the reward.
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