Rehab May Have Left Monteith More Likely to OD Body could have lost ability to tolerate heroin: doctors By Evann Gastaldo, Newser Staff Posted Jul 17, 2013 10:57 AM CDT 15 comments Comments Cory Monteith arrives at the 69th Annual Golden Globe Awards Sunday, Jan. 15, 2012, in Los Angeles. (AP Photo/Matt Sayles) (Newser) – Did rehab actually make Cory Monteith more vulnerable? Doctors explain to USA Today that drug users can be at higher risk of overdosing after leaving rehab if they aren't able to stay clean. Because heroin users build up a tolerance to the drug—which contributed to Monteith's death—they have to use more in order to feel any effects. But after detoxing, addicts' bodies can no longer handle those big amounts, and former addicts who relapse are likely to immediately revert back to the same big dose. That can kill them, one expert explains. As for the fatal dose of heroin, Monteith was alone in his hotel room when he took it, Vancouver police say, according to Radar. His death is particularly tragic, one friend tells Radar, in light of the fact that he previously kicked addictions to ecstasy and heroin. "Cory fought his demons and the demons won," another friend tells E!. "Cory wasn't going out and doing these things to have fun. He couldn't stop. He tried. He just couldn't." One of his demons: the fame that came from his role on Glee. It "was hard for him," yet another friend tells People, something "he never quite knew how to handle." It was the Glee cast and producers who convinced Monteith to go to rehab earlier this year when it became clear he was using heroin, TMZ reports, and Monteith was "grateful" for their support. Castmate and girlfriend Lea Michele has released a new statement through her reps, Celebuzz adds: She is "deeply grateful" for fans' support, and is "grieving alongside [Monteith's] family" while making arrangements.