Cory Monteith's mom says he was on pain medication for dental work before overdose death

Corey Monteith's mother revealed the "Glee" actor was taking pain medications for "massive" dental work before he died of a heroin overdose in 2013.

Ann McGregor told People she believes the pain medication derailed Monteith’s struggle with sobriety.

McGregor told People that Monteith checked into a rehab center in April 2013. Between the months of May and July, he had "massive' dental work done, for which he was prescribed painkillers.

"He had little teeth and they were all capped. He had a lot of medication in his system, which was not good for his body coming out of rehab," McGregor said in the interview published Wednesday. "He didn't have enough drugs in his system to kill him, but for some reason it did because of his intolerance [built up by periods of intermittent sobriety]."

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Monteith, 31, was found dead in a Vancouver hotel room in July 2013.

Authorities said he died of a lethal mix of heroin and alcohol. Traces of morphine and codeine were also found in his system.

He was known for his starring role as Finn Huck on Fox’s hit TV show, “Glee.”

McGregor told ABC News in 2014 that Monteith first began using drugs at age 15.

Cox Media Group