Probably alot. As someone mentioned Court , the Smashing Machine, Gregor Gillespie and Karo.
As a former addict, I dont like telling alot of people as they can use it against you and look at you crooked. With a fighter, they can more use it as an inspirational type thing, but even so, I imagine there are tons that just dont say hoot. You get hurt alot and then get percs/pain pills and no one can take them for an extended period and not get hooked When you get that opiate buzz, you are functioning at 110% and can do super human things train harder, longer and better.