The show's stars are accustomed to working hard – and letting loose after-hours
Credit: Lester Cohen/Wireimage

They were young, talented and thrust into superstardom almost overnight. For the cast of Fox’s Glee, life quickly went into “work hard, play hard” mode after the show debuted in 2009.

And before his sudden death at age 31 from a toxic mix of heroin and alcohol, Cory Monteith experienced both extremes.

Unlike the much-younger characters they portray on TV, “these aren’t high-school kids,” a Glee insider says of the cast. And they had easy access to the perks – and pitfalls – of fame.

“They had a lot handed to them,” says the source. “People will shut down clubs so they can dance. They’ve done their share of partying. That’s part of what it’s like to be a young celebrity.”

A second Glee source says of the show’s stars, “You would see them out. By no means were they not partying.” But the source adds that such after-hours revelry did not come until later in the series’ run: “This kind of partying wasn’t happening in their first season.”

And yet even in recent years, Monteith was not a fixture on the L.A. party scene. Adds the source: “I never saw him with them.”

Rather, the Canadian actor, who revealed his “serious” teenage drug addiction to Parade in 2011 and underwent rehab again in April, “was never very comfortable in bars because of his sobriety,” says a friend.

But Monteith and his roommates were known to host parties at his Hollywood Hills home. “Sometimes they were low key and sometimes they were ragers,” says a source.

“For every major holiday they’d have a big party, around 100 people, that died down around 2 or 3 a.m. Then pretty much every single weekend, they had small, 20-person parties that winded down around 3 or 4 a.m.”

But Monteith approached his Glee role with dedication, and several set sources say he was hard working and professional.

“He was not erratic,” says one show source, noting that the show’s shooting schedule “is all day every day for 10 months out of the year. Those cast members bust their ass singing, dancing, acting.”

Still, Monteith’s problems did not go unnoticed on set. Concerned for his health, Glee execs staged an intervention earlier this year, leading to his most recent stint in rehab. But the series insider says that his return to the same environment was cause for worry.

“To go to rehab for 30 days and back into the lifestyle that caused you problems in the first place doesn’t help,” says the source.

For much more on Monteith’s rise to fame, his past addiction struggles and his final days in Vancouver, pick up this week’s issue of PEOPLE, on newsstands Friday

Fans of Monteith’s may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver’s Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.

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