The 25-year-old is said to have completed treatment at a clinic five months ago, having also experimented with MDMA.
Reports of frequent absences whilst he was filming Seth Rogen's new fraternity comedy Neighbors emerged back in April, and a film source told an American site: 'It was common knowledge he was struggling with cocaine.'
'It was common knowledge he was struggling with cocaine.'
The site also reported that the High School Musical star and a group of friends caused $50,000 of damage in their room at the MGM Grand in Las Vegas during a cocaine-fulled party.
Zac is now said to be 'healthy, happy and focusing on his career', with a source revealing:
‘He's healthy, happy and not drinking. He's taking time to focus on working.’
An insider also told People: ‘He’s doing great. He's taking care of himself and it shows.’
Speaking at the Toronto International Film Festival recently, Zac reassured reporters: 'I'm good, real good.'
The actor’s squeaky clean image suffered a blow when he was spotted visiting a strip club in 2010, however he quickly redeemed himself on the Jimmy Kimmel show, joking:
‘The hardest part is calling your girlfriend before. It's like, how do you even start that conversation without feeling like an a**hole?'
But his then-girlfriend Vanessa Hudgens was understanding, with Zac revealing: 'She was fine with it.'