Las Vegas, NV, United States (4E Sports) – Chael Sonnen has retired from competitive mixed martial arts after he was pulled out of UFC 175 against Vitor Belfort on July 5 in Las Vegas for failing a drug test.
He was found to have used anti-estrogen medications anastrozole and clomiphene, which are among the World Anti-Doping Agency’s list of banned substances.
The 37-year-old Sonnen (28-14-1) took the substances to prevent side effects from getting off testosterone-replacement therapy, which was banned earlier this year.
Sonnen added he also used these for fertility reasons.
As he has a medical need for estrogen blockers, retirement from a 17-year professional career was his only option.
Sonnen specially thanked former UFC middleweight champion Anderson Silva, whom he challenged for the title in 2010 and 2012, and called him the single most important opponent he ever had.
“I couldn’t have gotten to where I am without this dance partner and that is, of course, Anderson Silva. I thank you for the opportunity and the memories,” said Silva.
He bested Silva through four rounds of a title fight before submitting to a triangle choke in the final round at UFC 117 in August 2010 .
Their rematch, which Sonnen lost via TKO in the second round at UFC 148 in July 2012, remains the highest-grossing UFC event ever held in Las Vegas with an attendance of 15,016 and a live gate of $7 million.
Sonnen also lost to Jon Jones for the UFC light heavyweight titleand had wins over Yushin Okami, Nate Marquardt, Brian Stann, Michael Bisping and Mauricio Rua.