Cory Monteith's Mom Blames Hollywood and Dental Work for 'Glee' Star's Death

McGregor opened up to People five years after losing her youngest son and said she believes his move to Hollywood to pursue acting combined with the "massive" dental work he underwent months before his death led to his relapse and eventual overdose.

McGregor said Monteith was always "advanced" for his age. He learned to read at the age of 3 and therefore skipped two grades in school. He began hanging out with an older crowd by his early teens. Monteith began drinking and smoking marijuana when he was 13. He went to rehab for the first time at the age of 15. He went again at 19.

"There was this disconnect because he was pushed so far ahead and always associated with older children, but he was still a boy," McGregor said of her son.

McGregor, who took Monteith to rehab both times, said, "He tried to keep everything from me because he loved me and wanted to protect me. He was just always so curious. And the darker world just drew him in."

Eventually, Monteith got sober and moved to Los Angeles, where he landed a starring role on "Glee." McGregor believes his move was detrimental to his sobriety.

"He wasn't ready for the Hollywood world," she said, acknowledging that her son began using drugs again in December 2012, seven months before his death. "Drugs were his way of checking out."

Monteith checked into a month-long rehab facility in April 2013, but between May and July of that year, he underwent "massive" dental work that McGregor believes also affected Monteith's sobriety.

McGregor believes Monteith's dental procedures and subsequently prescribed pain medications were the final straw for her son, whose body was discovered in a Vancouver hotel room on July 13 with traces of morphine, codeine and heroin in his system.

"He had little teeth and they were all capped," McGregor explained.

"He had a lot of medication in his system, which was not good for his body coming out of rehab. 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]," she claimed.

McGregor can still recall the chilling moment she heard that her son had died.

"I got a call from Lea [Michele, Monteith's girlfriend of over a year], and she was screaming on the phone," she said. "She was yelling, 'Is it true?! Is it true about Cory?!' And I said, 'What about Cory?' I had heard nothing. And then police knocked on my front door."

McGregor said she "went into a state of numbness" when she heard the news.

"I knew it was real, but there were times when I could lie to myself and say, 'He's in L.A. He'll call me soon,'" she said of dealing with the aftermath. "I'm still always hanging on edge. When you lose someone who is such a big part of you, you lose all purpose for living."