With news of Chael Sonnen's drug test failure and subsequent retirement, and the complete chaos that surrounded his match with Wanderlei Silva, then Vitor Belfort, at UFC 175, it's time to look back at the most notorious drug test failures in UFC history. We'll include all drugs, not just steroids, to mix things up a little. Drugs have wreaked havoc in MMA over the years, and some notable names have come out in favour of strong testing and enforcement, including one of the greatest of all time, Georges St. Pierre, who voluntarily submitted to more intense drug testing than most fighters during what would become his final match to date in the UFC. Roy "Big Country" Nelson has been another vocal opponent against PEDs (performance enhancing drugs) in the sport. Both these fighters are fan favourites, and a reflection of them in that sense - so why isn't the UFC pushing local athletic commissions to do more? Probably because it's not in their best interest. They don't lose money when a fighter is popped for drugs. They might get some bad press, but it never seems to hurt their bottom line. There are probably some solutions to this (bans from the sport for a second failure, for example, which might eliminate some popular names from the UFC roster), but that's a discussion for another day. For now, lets just take a look at some of the most notable, and in some cases, surprising, failures. One note to add, however: as this list is discussing UFC failures, there's a couple of dishonourable mentions to make. Royce Gracie, who started the whole damn show back at UFC 1, tested positive for anabolic steroids in 2007 after a match with Kazushii Sakuraba, which would be his final professional fight. The fight took place at Dynamite USA, co-promoted by EliteXC and FEG (the promoters of Hero MMA and K-1 kickboxing). At the time, there was no rule on the books to strip fighters of wins based on drug test results, so Gracie holds on to the win to this day. Also "worth" mentioning is King Mo's positive test while under the Strikeforce banner, which led to his release from the promotion in 2012. This test was also for anabolic steroids. Cyborg Santos, the most feared fighter in Women's MMA, was also popped for Stanozolol in 2012 while with Strikeforce. Those are just three big names outside the UFC, now lets take a look at who was found guilty while fighting in the big show.