Since retiring from boxing, Mike Tyson has been remarkably candid about his drug use.

The former “Baddest Man on the Planet” has openly discussed his use of psychedelics and cannabis on his podcast, Hotboxin’ with Mike Tyson. But in a recent appearance on The Katie Miller Podcast, the ex-heavyweight champ admitted to something even more serious: using fentanyl in the late '90s.

“That fentanyl stuff, I’ve done fentanyl before, in the late ’90s when it first came here,” Tyson shared, according to Complex. “It was for painkillers. I used to use it as a patch on my toe, but it was like heroin. Once you take it off, it wears off. You take the Band-Aid off, you start withdrawing and throwing up—just like if you were on heroin or something,” Complex reports.

When asked by Miller how he managed to avoid addiction, Tyson clarified:

“No, I did it quite a few times. But know what happened? It was illegal if it was caught in my bloodstream—it was a narcotic.”

Tyson recounted asking a friend—who happened to be a commissioner—whether the drug was allowed. “I told my friend, ‘Hey, can I use this?’... He looked it up and said, ‘Mike, that’s a narcotic. You can’t use it.’ I didn’t know that. I thought of it as a painkiller.”

Ultimately, Tyson said it was the fear of getting caught with an illegal substance that kept him from further use.

He also touched on his legal cannabis business and the lingering stigma surrounding drug use in the world of sports. He argued that cannabis is largely harmless, joking that the biggest concern is the user falling asleep.

This candid conversation comes just as Tyson is set to return to the ring. Last week, it was announced that he and Floyd Mayweather will face off in an exhibition match next spring. An official date, location, and broadcast details have yet to be confirmed.