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UFC welterweight contender Nick Diaz failed his post-fight urinalysis Saturday following his loss to Carlos Condit in their bout for the interim welterweight championship at UFC 143 at the Mandalay Bay Events Center, Keith Kizer, executive director of the Nevada Athletic Commission, announced Thursday.

Diaz, 28, who tested positive for marijuana, is a second-time offender in Nevada and, thus, faces a one-year suspension. He also tested positive for marijuana following a Feb. 24, 2007, victory over Takanori Gomi at a PRIDE Fighting Championship event held at the Thomas & Mack Center in Las Vegas.

Six weeks after the first positive test the commission fined Diaz $3,000 (20 percent of his $15,000 purse), suspended him for six months and changed his win over Gomi to a no-decision. The commission’s report in 2007 noted Diaz’s concentration of THC, the active ingredient in marijuana, was 175, three-and-a-half times the concentration level of 50 required under Nevada regulations to produce a positive test result.

“All results received thus far have been negative, except Mr. Diaz tested positive for marijuana metabolites,” Kizer said in a release Thursday. “A complaint for disciplinary action against Mr. Diaz has been filed.”