When Zac Efron entered rehab for alcohol abuse earlier this year, nobody batted an eyelid. Sure there was some concern, though the consensus was that here was a guy - one of the most popular actors in Hollywood - who was having a little trouble, though he'd be back on his feet in no time. He wasn't short of work, he wasn't short of cash. He'd be back.

Zac EfronZac Efron In Seth Rogen's 'Neighbors'

Only, it doesn't appear that Efron entered rehab for alcohol issues at all. In fact, it was far more serious than that.

According to TMZ.com, Efron completely a stint in rehab for a "serious cocaine addiction." Sources say the problem spiralled out of control during the filming of Seth Rogen's forthcoming comedy movie Neighbors, which was shot in a narrow time frame beginning in April and sees Efron play hard-partying frat guy who moves into a quiet suburban neighbourhood.

 According to insiders, the young actor was a no-show on a number of days. One source connected to the film said: "It was common knowledge he was struggling with cocaine." Three other sources confirm that Efron's problem was specifically with cocaine, though that he'd also tried Molly - a pure form of Ecstasy. 

Zac Efron NeighborsZac Efron Reportedly Struggled With Cocaine During The Filming of 'Neighbors'

The entertainment website also report how Zac and some friends went on a huge coke binge in a room at the SkyLofts at the MGM Grand in Las Vegas, causing around $50,000 of damage. 

The actor's representative said: "[I] don't think we'll be making comment."

Efron began acting professionally in the early 2000s, soon gaining fame as a teen idol following high profile roles on High School Musical, the WB series Summerland and the 2007 movie version of the Broadway musical Hairspray. Since then, he's added serious moves to his credits list, including Mr and Orson Welles, The Lucky One and now Neighbors. According to wealth website The Richest.com, Efron has a net worth of around $18 million.

Neighbors, written by Andrew J. Cohen and Brendan O'Brien, hits theaters in the U.S. on May 9, 2013.

Watch the Neighbors red-band trailer: