Brandon Rios failed his drug test following his loss via unanimous decision to Manny Pacquiao on Nov. 23 in Macau, China.

The boxer of Mexican-American descent has agreed to take random drug testing conducted by the Voluntary Anti-Doping Association (VADA). According to ESPN, Rios tested positive for stimulant methylhexaneamine, a banned substance which is used as a dietary supplement and as a performance-enhancing drug as well.

Exactly, what does methylhexaneamine do? Methylhexaneamine is a stimulant which is chemically related to ampethamines. Its effects are a little higher than a cup of coffee. James Conhen of the Henley Hawks also tested positive for such substance. Conhen was banned to compete for six months by the Rugby Football Union.

Dr. Margaret Goodman revealed to ESPN that the former World Boxing Association (WBA) lightweight champion weren't able to effectively finish the VADA program.

Hall of Famer promoter stated that Rios has already been notified after his bout with Pacquiao. Arum said that the Macau commission which synchronized the fight has already suspended Rios. However, the Top Rank promoter wasn't sure if the suspension lasts for 5 or 6 months.

Rios was aware that he had failed his drug test, but insisted that he was clean and that he never ingested anything that would be a contaminant.

"Like I told you man, I know I'm dirty," Rios told Yahoo Sports. "I'm not a dirty fighter," he added. Rios also stated that he is more than willing to take on any drug test 24/7. "I don't take no steroids, I don't take no drugs," said Rios. He said that he doesn't take diet supplements. He said that he is a natural strong fighter.

Rios also told Yahoo Sports that he had to urinate in a glass that was in his room because he didn't have a kit. Then, he transferred his urine from the glass to another cup that was brought to him 20 minutes later.

Arum revealed to ESPN that the banned substance found in Rios' urine post Pacquiao fight is not a steroid-related substance. Nevertheless, Arum stated that the substance was something that a fighter shouldn't have in his urine after a fight.

It has been reported that Rios passed all the drug tests prior the last one administered after the fight. It is not known whether Rios will make an appeal, but Arum said that he is allowed to do so.