"Big Brother" winner Adam Jasinski was just formally charged with possession of oxycodone with the intent to distribute -- and he faces 20 years in the slammer if convicted.

The federal indictment says Adam will have to hand over all the money and property related to his alleged pill-peddling -- which may include some of the $500,000 "Big Brother" prize he allegedly told cops he was using to fund his illegal activities.

Adam was arrested nearly three weeks ago for allegedly trying to sell a sock full of 2,000 oxycodone pills -- he's being held without bail because a judge considers him a flight risk.