Big Brother Winner ....LOSER...

Adam "Baller" Jasinski won "Big Brother" in 2008 -- and now he'll be sharing living space with even more strangers behind bars ... because cops say he used his $500,000 winnings to fund a drug dealing business.

According to FOX 25, Jasinski was busted Saturday night by the DEA with 2,000 oxycodone pills during an attempted drug deal in North Reading, MA. Jasinki was thrown in jail and charged with possession of oxycodone pills with intent to distribute.

Cops say Jasinski admitted to funding his illegal venture with his $500,000 winnings from the show. He'll remain in police custody until his next hearing on Thursday.

Adam faces up to 20 years in the slammer and a $1 million fine.