Anderson Silva tests positive for steroid, Diaz tests positive for marijuana

Former middleweight champion Anderson Silva has tested positive for an anabolic steroid, while Nick Diaz, who lost to Silva in the main event of Saturday's UFC 183, has once again tested positive for marijuana.

Silva was found to have Drostanolone metabolites in a test administered by the Nevada State Athletic Commission on Jan. 9 ahead of his unanimous decision victory Saturday at UFC 183 against Nick Diaz.

“Anderson Silva has been an amazing champion and a true ambassador of the sport of mixed martial arts and the UFC, in Brazil as well as around the world. UFC is disappointed to learn of these initial results," said the company in a statement released Tuesday.

The 39-year-old hadn't previously fought since suffering a leg injury in December 2013. He was also tested Jan. 19, according to ESPN's Brett Okamoto, although those results have yet to be released.

Commission chairman Francisco Aguilar told Yahoo Sports' Kevin Iole he didn't know why Silva's test results weren't received until after his fight.

"I would have had no problem calling the fight once I had this result," Aguilar said. "Those are not acceptable substances. But at the very least, by doing this out-of-competition test, we found this. We wouldn't have known had we not done the out-of-competition test."

Silva, who has never previously tested positive for steroids, still has a pair of post-fight test results to be made public.

Diaz was caught with marijuana in his system in a post-fight test, with the UFC releasing the following statement:

The UFC has been notified by the Nevada State Athletic Commission that Nick Diaz has tested positive for marijuana metabolites following his fight with Anderson Silva at UFC 183 on Jan. 31 in Las Vegas, Nev. The UFC has a strict, consistent policy against the use of any illegal and/or performance enhancing drugs, stimulants or masking agents by our athletes. 

As a result of his positive test, Diaz has been informed that he has violated the UFC Fighter Conduct Policy and Promotional Agreement with Zuffa, LLC. The UFC organization will fully respect the Commission’s final decision relating to Diaz at a disciplinary hearing set for February 17.

Diaz previously tested positive for marijuana after a Pride card in 2007 and again in 2012 after UFC 143. The 31-year-old has said he is a registered medical marijuana user in California.