The British middleweight (24-5) has suffered the misfortune of having been in the octagon against three fighters benefiting from testosterone exemptions: Dan Henderson, Sonnen and Belfort, accomplished veterans in their mid to late 30s at the time. He lost to them all, done in twice by KO or TKO -- the first of his career.
"It is obviously advantageous if you are on it," said Bisping, dropped by a Belfort leg kick in January 2013. "Look at somebody like Vitor -- you know he failed a drug test [in 2006]. And one side effect of taking steroids is reduction of testosterone production. So now he is being rewarded for cheating in the past. You also have to understand that, as your body gets older, certain parts slow down a little. On the flip side of it, you also got more ring experience.
"These older guys have had 30 or 40 professional fights, so they have more experience, plus they got the scientific supplementation. It is ridiculous. Of course, we're also not trying to hit a ball with a bat or throw it in a hoop. We're trying to knock our opponents out. So somebody is going to get hurt one day."
Indeed, the safety issue is dicey in a combat sport in which the endgame is inflicting enough bodily harm to send an opponent into submission -- occasionally via a blow to the head.
But whether naive or merely oblivious to the rumor mill, 34-year-old Bisping claims he was ignorant of his past opponents' testosterone exemptions when he stepped in the octagon. His suspicions about Belfort perked up after their 2013 fight in Sao Paulo.
"With Vitor Belfort, there was a whole cloud of secrecy regarding his drug test," Bisping said. "A lot of people saying he failed it. So I was obviously very intrigued and I contacted the UFC and they said, 'No, he hasn't failed it, but he did have a TRT exemption certificate."'
Only a month after the fight, amid a firestorm of rumors, the UFC issued a statement revealing Belfort had been on a medically approved TRT regimen under the supervision of a Nevada physician. Coming two years after Belfort now acknowledges having begun TRT, the release said the regimen had been initiated after a diagnosis of "hypogonadism, or low testosterone."
Despite his current hardened stance, Bisping said he likely would not have balked at challenging Belfort even had he known of his testosterone supplementation. He said, though, that friends told him after the fight of having feared for his well-being because of the "sheer size" of Belfort.
"The guy was so heavily muscled," Bisping said. "At the time, you are a fighter and you believe you are going to win. So I never thought about it. Looking back, you can clearly see he was on something stronger than a frosty shake."
Nor is the fiery Brit the lone voice of suspicion in a sport in which doping has evolved through the years -- as in many others -- from hard-core steroids to growth hormone and designer drugs. Or what one UFC contender referred to collectively as "blue gasoline -- the extra fuel."
The twist is that no other sport appears to have so freely handed out passes to TRT.
Reporter Josh Gross contributed to this report. Mike Fish can be reached at email@example.com