Former UFC heavyweight champion Brock Lesnar has informed the mixed martial arts promotion that he is retired from competition.
The UFC confirmed the 39-year-old Lesnar's decision Wednesday.
Lesnar returned from a 4½-year MMA absence last July to beat Mark Hunt at UFC 200, but the result was overturned after Lesnar failed two doping tests. He was subsequently suspended from competition for a year by the U.S. Anti-Doping Agency, which administers the UFC's doping policy.
Lesnar's decision to retire means he has been removed from USADA's drug-testing pool, which monitors the fighters year-round.
If he decides to return to competition, he would have to serve the remaining five months of his suspension.
The decision doesn't affect Lesnar's professional wrestling career, where the multitalented athlete has spent most of the past five years. He is scheduled to perform for the WWE at WrestleMania in Orlando on April 2.
Lesnar fought for the UFC just eight times, but he became one of the biggest pay-per-view stars in the sport's history during his brief run. The former NCAA wrestling champion and WWE star drew millions of new fans to the young sport with his hulking presence and violent skills.
He made a guaranteed $2.5 million purse for his victory over Hunt last year, along with likely millions in undisclosed bonuses. But Lesnar failed a drug test taken before his fight and another on fight night. He tested positive for clomiphene, a banned substance under USADA rules.
Lesnar won the UFC heavyweight title in just his third fight for the promotion, beating Randy Couture in November 2008. He defended the belt twice before losing it to Cain Velasquez in October 2010, and he lost to Alistair Overeem in December 2011 in his final fight before his 2016 comeback.
He also endured serious health problems that curtailed his MMA fighting prime, including a bout of diverticulitis.