Sonnen will presumably be suspended, and a second middleweight title fight between Sonnen and Silva -- which undoubtedly would have been among the biggest fights for the UFC next year -- may need to be scrapped.
"[Sonnen] received his notice yesterday," California State Athletic Commission Executive Officer George Dodd told Sherdog.com.
There is no word on which banned substance Sonnen took, but it was reportedly a performance-enhancing substance and not a drug of abuse.
Sonnen, who gained widespread attention for his constant trash talk leading up to the fight with Silva, has not commented on the story. But there's no doubt that this will change his reputation among MMA fans. Sonnen was viewed after fighting Silva as the hard-nosed fighter who took it to the UFC's most unbeatable champion for five rounds, and even though Sonnen did tap out in the fifth round, he was widely acclaimed for the way he dominated Silva for 22 minutes leading up to that submission. Now he'll be viewed as a cheater.