Another UFC fighter has come out with an big statement estimating the % of UFC fighters who use performance enhancing drugs (PEDs). Welterweight contender Dong Hyun Kim aka "Stun Gun" did an interview with the South Korean outlet MFight and said (translation via Middle Easy):
While a lot of people believe doping tests work, just like a breathalyzer test you can get away with it by just controlling timing. Most of the steroids user just cycle and get by the tests. It's almost like other athletes look down on you as an idiot if you don't do steroids. It's like non-users are bicyclists while steroid users are racing with motorcycles. But I am one of those "idiots" that don't use performance enhancers. I would say 90% of UFC fighters use performance enhancers.
Kim isn't the first UFC fighter to come out with an informal estimate of the % of competitors using the juice.
Dennis Hallman came out with a 50% number. Roy Nelson says many past opponents have confessed to him. Krzysztof Soszynski has staked his claim at 80%. Nate Diaz went there with "everyone" in the UFC is on steroids(presumably except him and his brother Nick).
I don't think Kim has any special insight given that he trains mostly in South Korea, half a world away from most of his competition. Nonetheless, it's obvious there is a PED issue in the UFC.