Zac Efron allegedly sought treatment this year in a rehabilitation center for cocaine addiction.
And the Parkland star is said to have completed his stint in the treatment facility around five months ago.
A source told gossip website TMZ.com that the actor spiraled out of control while filming Seth Rogen's movie, Neighbors, in April, and was a no-show on the 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 that 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 filmmaking and I feel blessed to have been a part of it."
Zac dated his High School Musical co-star Vanessa Hudgens for almost four years until December 2010, and was most recently linked to 19-year-old actress Maika Monroe.