I pretty much agree with Rampage's opinion on marijuana -- but I think he's been listening to Joe Rogan a little bit - lol.
I do agree with eyebrow-Eddie that sterioids (PEDs) runs rampant in the sport - probably a lot more rampant than we think. I think it's the same as baseball, basketball, football, etc. Fans of the sport refuse to believe it's in their sport -- but I'm on the other side of the fence. Maybe I'm just a cynic... I dunno.
You're not a cynic it's just a reality of certain sports. Any sport where strength and power are crucial is full of PEDs, including UFC. The good news is that skill beats PEDs. My eyes tell me that Anderson Silva is natural, and look at the list of the Testosterone Brigade that he's beaten:
Bonnar, Sonnen, Marquardt, Henderson, Irvin, Belfort, Griffin...