LAS VEGAS -- Former UFC middleweight champion Anderson Silva, widely considered the greatest mixed martial artist of all time, has been suspended one year by the Nevada State Athletic Commission because of multiple failed drug tests.

Silva, 40, appeared before the NSAC for a disciplinary hearing Tuesday; he had failed several tests before and after his Jan. 31 fight against Nick Diaz at UFC 183.

The one-year suspension is dated retroactively to Jan. 31. He also was fined $380,000 and must submit a clean test before he can be re-licensed. The result of the fight, a unanimous decision victory for Silva, changes to a no-contest.

The UFC backed the Nevada commission's decision. The world's dominant mixed martial arts promotion instituted a comprehensive drug testing policy earlier this year in partnership with the U.S. Anti-Doping Agency.

"The UFC organization maintains a strict, consistent policy against the use of any illegal and/or performance-enhancing drugs, stimulants or masking agents by its athletes, and fully supports the Commission's ongoing efforts to ensure clean competition by all MMA athletes," the organization said in a statement. "The UFC recognizes Silva's great career and looks forward to his return to the Octagon in 2016."

Silva (33-6) maintained his innocence throughout the disciplinary hearing, stating the failed drug tests were a result of a contaminated sexual-performance enhancing drug he received in an unmarked vial from a friend who lives in Thailand.

The Brazilian fighter tested positive for drostanolone, an anabolic steroid, in addition to a form of androstane, on Jan. 9. He tested positive for drostanolone again on Jan. 31, as well as anti-anxiety medication, which also is considered a banned substance.

He was still allowed to compete on Jan. 31 despite the previously failed test because the NSAC had not received the results from its lab in Salt Lake City.

"I am human and made mistakes," Silva told the commission through an interpreter. "It definitely was a mistake. If I had known this supplement that I was taking for something else would have caused this sort of problem, I never would have taken it."

Anderson Silva tested positive for drostanolone, an anabolic steroid, and a form of androstane, on Jan. 9. He tested positive for drostanolone a second time on Jan. 31, and anti-anxiety medication, which is banned. Josh Hedges/Zuffa LLC/Getty Images

Silva's attorney, Michael Alonso, argued before the commission that because the drostanolone came from a contaminated sexual-performance enhancer, Silva shouldn't face discipline. He attributed the androstane to a contaminated supplement as well, but couldn't identify which substance Silva was on at the time that produced the result. At no point did Silva's defense present the NSAC with documentation regarding its findings of any contaminated substance.

The NSAC took further issue with Silva's failure to reveal supplements he was on leading up to Jan. 31 on a prefight questionnaire. Silva said he did not reveal his use of the sexual-performance enhancer because of privacy concerns. He said he did not list the anti-anxiety medication, which his manager, Ed Soares, said was prescribed well before the fight, because he hadn't used it regularly and did so only the night before the fight to help him sleep.

NSAC chairman Francisco Aguilar said there were "major inconsistencies" in Silva's defense. Silva contradicted himself at one point regarding the exact dates on which he allegedly consumed the sexual-performance enhancing drug.

Silva's defense also attempted to rely on a series of tests the fighter passed both before and after the Diaz fight. On Jan. 19, Silva passed an unannounced blood and urine test administered by the NSAC. He also passed two tests on the night of the contest, as the NSAC utilized two different methods to test him and sent the samples to two labs. The NSAC found, however, that the negative tests had no bearing on the positive ones.

Silva previously had never failed a test in his professional career, which dates to 1997. This was the first time, however, he was subjected to random, out-of-competition testing, which the NSAC started to utilize somewhat regularly in the past year.

Immediately prior to the NSAC's unanimous vote for a one-year suspension, commissioner Anthony Marnell said he didn't believe that Silva's testimony regarding the failed tests was complete.

"I don't feel like we're getting the whole story," Marnell said directly to Silva. "I'm not going to say it's a lie. I'm not going to say you're not telling the whole truth under oath -- but we're not getting the whole picture here.

"I'm not taking anything away from Mr. Silva's excellent career, but this is the first time he's been subject to enhanced testing. It's hard to put a lot of credibility into his prior test results -- not his career, his test results. I feel there is some intention here to use a product to come from a devastating injury. Not saying that's it, but I have that feeling in my stomach."

Silva returned from a 13-month injury layoff to fight Diaz. He suffered a broken left tibia and fibula while throwing a kick during a fight against Chris Weidman at UFC 168 in December 2013.

The Associated Press contributed to this report.