A week after he was arrested for DUI, Matt Hardy was thrown back in the slammer -- his third time in jail in a month -- and the search warrant makes it clear ... Matt has a major drug problem.
According to search warrant docs obtained by TMZ, it all started with a 911 call last Wednesday -- placed by Matt's model girlfriend, Reby Sky, who was worried Matt "was strung out on pills and needed help."
Police came and Matt's GF led them to a secret safe containing several prescription painkillers.
Police then obtained a search warrant -- and according to cops, when they raided his house they found 20 vials of anabolic steroids and some ecstasy.
Law enforcement sources tell TMZ, Matt wasn't home at the time of the search so they couldn't arrest him on the spot ... he turned himself in yesterday.
Hardy -- who bailed out soon after his arrest -- posted an emotional YouTube video last night (below), saying he's enrolling in a 3-month rehab program paid for by the WWE, as part of its former talent rehabilitation assistance program.