It was not Monteith's first time in rehab. He received treatment when he was 19 and had previously talked about his addiction struggles, saying he had a serious problem and took just "anything and everything."
He told Parade magazine in 2011 that he was "lucky to be alive."
Monteith, who turned 31 on May 11, starred in "Glee" as a high school football player who puts his status and popularity at risk to join the glee club and its outcast members.
The show, with its pop music-based song-and-dance numbers and high-profile guest stars including Gwyneth Paltrow, became an immediate hit and made stars of its relatively unknown cast.
The series, which debuted in 2009, is in its fourth season.
On his Twitter account, Monteith described himself as "tall, awkward, canadian, actor, drummer, person."
In a 2010 interview with The Associated Press, Monteith was upbeat about life. He said that if "Glee" were to be canceled he would be OK.
"I've never been afraid of working," he said. "I've never been afraid of auditioning for jobs. Obviously, I've never been afraid of anonymity. I was happy (before 'Glee'). I'm happy now. I guess I'm well adjusted."
Monteith was among the "Glee" actors who remained series regulars as their characters graduated high school and moved on to other adventures.
According to his biography on Fox's website, Monteith was born in Calgary, Alberta, and moved to Vancouver Island as a child. Before turning to acting, he held a variety of jobs including Wal-Mart greeter, school bus driver, roofer and cab driver.
Monteith's TV credits included roles on the series "Kaya" and "Kyle XY" and guest appearances on "Smallville," ''Supernatural," ''Stargate," ''Flash Gordon" and "Interns." His film credits included "Final Destination 3," ''The Invisible," ''Deck the Halls" and "Whisper."