Ahead of Canelo Alvarez‘ rematch with Gennaday Golovkin, Alvarez tested positive for performance enhancing drugs. The mutually agreed upon drug screening from both boxers which was performed by the Voluntary Anti-Doping Association found traces of clenbuterol in Alvarez system. Clenbuterol is a steroid often used to treat asthma and has been found to have anabolic benefits in rats.

Canelo has been training in Guadalajara, Mexico and performed his drug test between February 17 and February 20 in Jalisco, Mexico. Alvarez and his team believe the traces of clenbuterol came from contaminated meat that has affected many Mexican athletes in recent years due to a mass contamination across the country.

“I am an athlete who respects the sport and this surprises me and bothers me because it had never happened to me,” Alvarez said in a statement. “I will submit to all the tests that require me to clarify this embarrassing situation and I trust that at the end the truth will prevail.”

In a letter obtained by ESPN, The Sports Medicine Research and Testing Lab determined that the levels of clenbuterol found in Alvarez’ system is consistent with the amounts expected from meat contamination. However, the Nevada State Athletic Commission will make the final determination on if Alvarez will be eligible to fight this Spring.

According to the National Drug Strategy, “Some animal studies have shown that using a stimulant like clenbuterol has the ‘anabolic effect’ of increasing muscle mass and body weight by enhancing muscle protein synthesis in rodents. However, no human studies are available on whether clenbuterol can increase strength or power.”

The drug is often used as a fat burner that helps raise body temperature and can temporarily speed up an athlete’s metabolism to help burn calories faster.

The Alvarez, GGG rematch is scheduled for May 5 at the T-Mobile Arena in Las Vegas. Their last fight ended in a highly controversial draw that left the Middleweight title belt with the Kazakhstan born boxer, Golovkin.

Should the fight continue as planned, this will be Golovkin’s 20th title defense — and if he should beat Alvarez, The 35-year-old will break the record for most title defenses which is currently held by “The Executioner” Bernard Hopkins.