How do we know? Failed a drug test in MMA competition and eventually admitted use. Speculation about Ken Shamrock's steroid use went back long before he went back into pro wrestling. In the UFC, nobody else looked like him. Even the most athletic of the life-long martial artists didn't look like they were training for cosmetic appearance the way Shamrock appeared to be. He was huge and cut like a super hero out of a comic book. Unlike the other early UFC stars, he had a unique combination of looks and legitimate skills. Throw in his existing pro wrestling experience, and it made all the sense in the world for WWE to go after him when the money in the UFC got bad.Shamrock went back to MMA after a neck injury ended his WWE career. He probably made good money at the time, but he should not have been in real fights with his spine as messed up as it was. He won just five of his 15 post-WWF fights, with his failed drug test coming after one of the wins. His adopted brother and former training partner Frank believes that having to get off steroids (or take much lower doses) to pass athletic commission testing sapped too much of his confidence.