Well, Nick Diaz tested positive for THC after beating Takanori Gomi, and was stripped off his win. Tito Ortiz and Kendall Grove (former training partners) both have admitted to puffing the magic dragon. Other than that, I don't know. However, Tito did mention in an interview that there are other fighters who smoke the herb. I'm sure more do/have, but they probably only do the day after their fights, so they don't fail their drug tests like idiots.