If you follow sports outside of kickboxing you know how much of a problem performance enhancing drugs are. Hell, we even had our first positive drug test at a GLORY event at GLORY 17. It is kind of the nature of sports, in a way; you want to be bigger, better, stronger and to be able to compete. If you think that everyone else is doping, you find yourself needing to do it to compete. There haven't been a ton of cases of kickboxers in trouble for PEDs, but there have always been rumors and accusations.
Remy Bonjasky this weekend added fuel to the fire by claiming that 80 - 90% of K-1 fighters were juicing and that he was never a part of that club. He cites wider jaws and added muscle mass as visual cues that someone is on steroids, which seems like a pretty broad statement.
"I do not use and have never done so. I've always said that if I do not succeed in a normal way, I should quit [fighting.] I always want to win and if I can not win with eating normally then it stops." [source]