St-Pierre, 32, wanted to be a game-changer by offering to pay for Johny Hendricks to be tested by the Voluntary Anti-Doping Association (VADA) prior to their UFC 167 bout.
He said the UFC wasn't very supportive of his actions.
"That's one of the reasons why I stopped fighting," St-Pierre said. "Not really to teach them a lesson, because that would also punish me. I wanted to do something for the sport. I love the sport. I see the direction it's going, and I don't think it makes any sense. This is stupid."
St-Pierre spoke carefully to avoid bashing the UFC or Dana White too much, but it was clear he wasn't happy.
"The only thing I want to say is, I wanted to do something to help those who are honest in the sport," St-Pierre said. "Believe me or not, I never took drugs in my life. I'll take a lie detector test, I don't care. I'm for anti-doping tests. I think it's a big problem in the sport. This is a relatively new sport. There's one organization that has a monopoly, so the fighters don't have much power. They can't really talk because if one says what he thinks, he will get punished.
"If we want the sport to be accepted worldwide, like baseball, hockey, football, soccer, I believe [drug testing] is the thing to do. I think it's just a matter of time before it happens, it's just that I tried to make it happen now. Maybe they didn't like the idea because if I did it now, it would lead to others doing it and maybe that's not something they wanted to happen.
"It disappointed me. You know that there are things I can't say. I'm holding back. I'm a public person."
St-Pierre said he's open to a return to action if things change someday down the road.
"No wants to talk about [drugs in MMA], but I think we need to talk about it. It's a problem," St-Pierre said.
"I wanted to remain diplomatic, but unfortunately there were people who weren't ready to change things. I'm certain it's a question of time. And maybe if things change one day, I'll return."