Brock Lesnar has been informed his UFC 200 fight-night sample has the same banned performance-enhancing substance that he tested positive for on June 28, UFC announced Tuesday.
An official with knowledge of Lesnar's samples identified the banned substance as the fertility drug clomiphene, one of the two banned substances found in a June sample taken from former UFC light-heavyweight champion Jon Jones.
Lesnar, 39, defeated No. 8-ranked heavyweight Mark Hunt by unanimous decision in the co-main event of UFC 200 on July 9, a celebratory return from a five-year absence by the former heavyweight champion whose career was hampered by a battle with the intestinal disorder diverticulitis.
Last week, it was announced that the U.S. Anti-Doping Agency found Lesnar's June 28 sample positive for a banned substance that has yet to be officially revealed by the Nevada State Athletic Commission.
Lesnar remains under contract with WWE and is scheduled to participate in SummerSlam next month at New York City's Barclays Center.
He left the door open to a possible UFC return after defeating Hunt, but the positive tests results could lead to an extended ban that would ensure the July 9 fight at T-Mobile Arena in Las Vegas was his last in the organization.
In a statement revealing Lesnar's positive drug test, a UFC spokesman wrote: "USADA, the independent administrator of the UFC Anti-Doping Policy, will handle the results management and appropriate adjudication of this case.
"It is important to note that, under the UFC Anti-Doping Policy, there is a full fair legal review process that is afforded to all athletes before any sanctions are imposed. The Nevada State Athletic Commission also retains jurisdiction over this matter as the sample collection was performed at UFC 200 in Las Vegas."
UFC 200 was previously marred by the company's decision to pull former light-heavyweight champion Jones off the card after he submitted a sample with substances that the Nevada commission identified this week as clomiphene and letrozole.
"They both boost testosterone levels," said Victor Conte, the famed former head of the steroid lab BALCO. "Clomiphene is a PED. It enhances performance. It can increase testosterone by 50%. I personally used it during the BALCO days.
"The [letrozole] blocks conversion of testosterone to estrogen … making you stronger, faster and aiding your recovery [between workouts]. … It'd be like increasing the amount of water going into a bathtub with [clomiphene] and reducing the size of the drain with the [letrozole]. The effect is more water in the bathtub —more testosterone. The drugs are synergistic."
Conte said he's "never heard" of either substance showing up in nutritional supplements.
"Either bring in the supplement and have it tested, or that excuse is a smoke screen," Conte said.
Lesnar called Jones' actions "unprofessional" at a public appearance the day after Jones was pulled from the card.