As per Dave Meltzer's site:
An interesting name has surfaced in the latest update to the UFC/USADA drug testing program database, updated weekly as more fighters are tested. That name: the "American Gangster" himself, Chael Sonnen.
Sonnen retired from MMA competition following a failed drug test prior to his UFC 175 bout, which was scheduled to be originally against Wanderlei Silva, and then against Vitor Belfort after Belfort replaced Silva, who fled from a drug test himself. He was later suspended from competition for two years by the Nevada State Athletic Commission for failing multiple drug tests for five different substances.
As a retired fighter, Sonnen was not subject to random testing under the new UFC Anti-Doping Policy, which came into effect last year. Had Sonnen not officially retired, he could have, and likely would have, been tested multiple times. However, if a retired fighter intends to return to competition, they must go through drug testing for four months before the date they intend to return.
With Sonnen's name now being in the testing protocol, it opens him up for returning to action in four months which happens to be around the time the UFC makes its debut in New York at Madison Square Garden for UFC 205.
Sonnen last fought in November 2013 at UFC 167, a loss to Rashad Evans.
Sonnen recently confirmed his intentions of staying retired during an interview with our own Dave Meltzer and Bryan Alvarez, but as he has so often proven, you never know what he's up to. Now that he's entering the testing protocol, never say never on the chance of him returning.
In Chael we trust 
Maybe I'm the only one, but I would love to see and aging, no dick pill, Anderson silva fight and aging, no "medicine", Chael Sonnen.
Macallan12 - Maybe I'm the only one, but I would love to see and aging, no dick pill, Anderson silva fight and aging, no "medicine", Chael Sonnen.You are far from the only one
Yeah anderson vs chael (ped free) 3 would be awesome 
MartialArtsMixed - Yeah anderson vs chael (ped free) 3 would be awesomeHell ya, let's do it
Maybe that's the "Big Fight" Tim Kennedy says he has lined up in November??
Chael vs vitor!
Silva finished Chael twice. I bet Chael calls out Bisping if he's still champ since Bisping seems interested in avenging losses as champ.
Chael takes Anderson down and wins a UD over 3 rounds (cause they cant do five sans PEDs). Chael raises Andersons hand after and says hes the best ever. They have a bbq with medium rare steaks. Roll Curtain.
Lmao at no medicine chael