UFC women's bantamweight contender Mayra Bueno Silva, in an Instagram post Monday, said she failed a drug test taken the week of her fight against Holly Holm last month.
Bueno Silva is facing discipline from the USADA, the UFC's anti-doping partner, and the Nevada State Athletic Commission (NSAC).
In her post, Bueno Silva wrote that the substance she tested positive for is "consistent" with the doctor-prescribed medication she takes for ADHD. She noted that she is cooperating with the USADA and NSAC, and has sent them both documentation about her medical history.
"I have never in my life taken a substance to enhance my ability in or outside the cage," Bueno Silva said.
"Per Ms. Bueno Silva's social media post, we encourage all athletes with a diagnosed medical condition to apply for Therapeutic Use Exemption (TUE), which would allow an athlete to compete without risk to their health and safety by stopping the use of needed medication," USADA said in a statement.
USADA also noted Silva's cooperation and said it would "work thoroughly to uncover the facts."
Bueno Silva (11-2-1) was one of the fighters in contention for the next UFC women's bantamweight title fight. The belt was vacated earlier this year by the retired Amanda Nunes.
Bueno Silva, 31, beat Holm via second-round submission. The NSAC could overturn that result to a no contest. The Brazilian-born fighter, who trains out of Florida, has won four straight.
"I look forward to fighting again for the best organization in the world," Bueno Silva said in her post. "I am the next champion and I am ready to fight."