How bad is the steroid "epidemic" in mixed martial arts (MMA)?

Bad enough to assume that at least half the Ultimate Fighting Championship (UFC) roster is using the gear, according to UFC color commentator Joe Rogan, who talked about some of the high-profile drug busts in recent weeks during his weekly podcast.

MMA Fighting with the transcription:

"The UFC and MMA in general is a steroid epidemic. They've started this really stringent testing and everybody is getting popped. They're just getting popped left and right. It's one of the things fighters have been saying for a long time, that everyone is on steroids, a huge percentage. Give a number 50, 60 [percent]. Whatever the fuck it is that are on steroids. The reality is, this whole steroid epidemic, one thing we have to recognize, the use of steroids is less than 100 years old. There's always been substances that people have taken, but the actual use of anabolic steroids in human beings is relatively recent in human history. I think as time goes on, they're going to create more powerful and crazier shit and it's going to get to the point where you're going to test negative because you're not on it anymore but your body will forever be changed."

Not that steroids are relegated to MMA.

Unfortunately for our still-growing sport, the bubble in which it operates is much smaller, allowing fans to have a more intimate association with each competitor. It also doesn't help when the fighter widely-considered to be the greatest of all time is failing drug tests in the twilight of his career.

Which according to Rogan, is just a small piece of the steroids pie.