This guy doesn't look like he would use steroids

Oh wait he did. Antonio Silva, the EliteXC heavyweight champ, tested positive for boldenone, an anabolic steroid that has been seen is horses and Stephan Bonnar. Most interesting thing about this steroid (according to wikipedia I don't have more time to fact check right now) is that it has a 1.5 year half life. Meaning that Silva could've taken this thing a year ago and the positive test occur now. Not a very smart drug to use. But there is more, it also lacks a progesterone receptor interaction (again according to wiki not a lot of time here). Progesterone is one of those female hormones, so by taking this drug you hope to avoid in feminizing side effects.