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The Nevada State Athletic Commission has confirmed that recently retired mixed martial artist Chael Sonnen tested positive for four banned substances on June 5.
Sonnen, 37, who retired earlier this month after a previous failed drug test was announced, tested positive for human growth hormone, erythropoietin (EPO), anastrozole and human chorionic gonadotropin (hCG).
NSAC chairman Francisco Aguilar confirmed the test results to ESPN, following an initial report by MMAFighting.com.
"Yes, the Commission is aware of other prescribed medications I was taking and I will not challenge their allegations. I will co-operate with the Commission and look forward to having a dialogue about how fighters who transition off [testosterone replacement therapy] can avoid violating any rules," Sonnen said, according to MMAFighting.com.
HGH is often used to build muscle for athletic performance. EPO causes bone marrow to produce more red blood cells, which can increase stamina and endurance. The substance hCG, which Sonnen admitted to taking earlier this month, is typically used to kick-start testosterone production in the body.
Sonnen (28-14-1) was scheduled to fight Vitor Belfort at UFC 175 on July 5 in Las Vegas but was pulled from the card on June 10 after the NSAC confirmed he had failed a random test administered on Memorial Day weekend in Las Vegas.
That initial test produced a positive result for anastrozole and clomiphene, both of which are classified as antiestrogenic. Sonnen announced his retirement from MMA the day after the test results were made public.
On June 5, however, the NSAC ordered a second blood and urine test from Sonnen, who was still licensed to compete at that time. The results of those tests were not available until this week.
On June 17, the NSAC temporarily suspended Sonnen's license to fight in the state of Nevada. The commission most likely will take disciplinary action against Sonnen at a meeting on July 23. Both failed tests will be taken under consideration.
"We were made aware of a second random test conducted earlier this month which resulted in a positive test for additional banned substances," the UFC said in a statement on Saturday night. "Chael will have the opportunity to appear in front of the Nevada athletic commission next month. Through a statement released to media tonight, he's pledged to co-operate.
"Our stance on the subject remains absolutely the same. We support the commission and will continue to ensure all UFC competitors compete on an even playing field, free of performance enhancing drugs and banned substances."
Sonnen had stated he had taken the antiestrogenic substances to avoid side effects from getting off testosterone replacement therapy, which the NSAC banned from combat sports earlier this year.
A three-time UFC title contender, Sonnen is scheduled to meet Andre Galvao in a no-gi jiu-jitsu match at Metamoris 4 on August 9 in Los Angeles.
This article originally appeared on ESPN.com