Drug testing in the UFC was effectively the wild, wild west when Georges St-Pierre first walked away from the sport in 2013.

Back then, in the era of testosterone-replacement therapy, out-of-competition drug screening was nonexistent and commission-mandated testing was generally viewed as an IQ test more so than anything else. But all of that changed in July 2015 when the UFC and the United States Anti-Doping Agency (USADA) partnered to create one of the most comprehensive drug-testing programs in all of sports. Ever since, failed drug tests have become commonplace in the UFC while the number of suspensions handed out by USADA has ballooned with each passing month.

But St-Pierre is confident that plenty of cheaters still remain in the UFC.

“Even now, it’s still easy to [cheat]. Even now,” St-Pierre said recently during an appearance on The Joe Rogan Experience.

“Let’s say I want to have an injection of a product that will last in my body for two days or one day. So I know that particular day I cannot be tested, because if I am, I’m screwed. So I put on my [USADA] whereabouts [app] that I’m traveling to freakin’ Antarctica or anywhere, somewhere that is believable, and then I come back two days after. That substance will stay in my body for a certain period of time, but the effect of it will last maybe a month. And now we’re talking about performance enhancing drugs — people, they misunderstand this.

“They go, ‘Well yeah, but it still doesn’t make a difference.’ Yes, it does make the different in an athlete,” St-Pierre continued. “And the reason, in the eighties and before, [PEDs gave] you more power, more stamina, more endurance. Now, man, with the technology, they have stuff that will change your reaction time, your confidence, your reset time. And this is a huge, huge application, man. If you play baseball or you’re fighting, you see the things coming, you have your reaction time, you’re sharper in the brain. What makes a guy athletic, it’s not his muscle. The reason why Usain Bolt ran faster — there’s many reasons why, but one of the main reasons is because his brain, his nervous system is faster.

“And if you make your nervous system better and more competent, you’re a better athlete. You’re a better fighter, you’re a better baseball player. You’re a better person, in a way. Of course that effect is limited, but there’s still the muscle memory thing that will last and it could last forever.”

St-Pierre, 37, has long been one of the staunchest anti-PED voices in the UFC. He spearheaded a push for improved drug testing during his heyday as welterweight champion, including memorably debating Johny Hendricks for months over a desire to have out-of-competition drug testing administered by the Voluntary Anti-Doping Association (VADA) ahead of the pair’s November 2013 title fight at UFC 167.

In that case, Hendricks initially agreed to St-Pierre’s request of VADA testing but then changed his mind, leaving St-Pierre furious at both Hendricks and the UFC.

Whether by coincidence or circumstance, Hendricks has lost five of his six fights since the UFC-USADA partnership came into effect — and St-Pierre was asked point-blank on the show whether he believed “Bigg Rigg” was cheating in the lead-up to UFC 167.

“You asked me if I think he was taking [PEDs]. I don’t know,” St-Pierre said. “I have suspicions, but it’s not right if you don’t have the evidence to accuse someone. And even today, do I think there’s a lot of guys who take steroids and performance-enhancing drugs? Yes. And I have an idea of who, and I’m pretty — like, just for my gut feeling — 99.9 percent sure. But I don’t have the evidence.

“It’s not what you think, it’s not what you know. It’s what you can prove. And I don’t know. I’m in the game, I’m talking to a lot of people. Between fighters, we know who does. There’s only a few handful of people who do the whole thing [in regards to supplying PEDs]. One guy could do this team, this team, this team, and one other guy can do two teams. The word goes around, man. Especially when you’re a complete fighter, the word goes around.”

St-Pierre added that although he believes the current drug testing setup in the UFC is a massive improvement over how things used to be, USADA can only do so much.

After all, he said, the technological capabilities of cheaters will always be one step ahead of those who are looking to stop them.

“It’s very hard to catch people. So like I said, it’s easy to take something,” St-Pierre said. “There is a always a chance that you get caught, but if I would do it, that’s how I would do it. I would pretend I’m going to Antarctica, get an injection, then I come back and I’m good.”