Zac Efron allegedly sought treatment in rehab for a cocaine addiction this year.
The Lucky One star, who previously dated his High School Musical costar Vanessa Hudgens for almost four years until December 2010, and was most recently linked to 19-year-old actress Maika Monroe, reportedly completed a stint in a treatment facility approximately five months ago.
A source told gossip website TMZ.com the actor spiralled out of control while filming Seth Rogen's movie Neighbors in April and was a no-show on set for a number of days.
The insider added, "It was common knowledge he was struggling with cocaine."
A spokesperson for Zac said, "Don't think we'll be making a comment."
Another source told People.com the 25-year-old actor is "doing great" and is now clean and sober, adding, "He's taking care of himself and it shows."
An insider also told E! News, "He's healthy, happy and not drinking. He's taking time to focus on working."
Zac recently appeared at the Toronto International Film Festival to promote his new drama about John F Kennedy's assassination and said he feels like his career is moving in a new direction.
He told USA Today, "It's really a surreal experience for me. It feels very mature and really interesting. It's a whole different kind of film-making and I feel blessed to have been a part of it."