updated 09/25/2013 AT 1:20 PM ET
•originally published 09/25/2013 AT 2:30 PM ET
He was an A student in his Arroyo Grande, Calif., high school – a theater kid who hit the big time as the fresh-faced teenaged star of Disney Channel’s High School Musical phenomenon. There were no public displays of bad behavior, no drunken arrests or barroom brawls.
But with fame came a partying lifestyle that continued to escalate until Zac Efron quietly sought help in rehab.
“He was partying a lot,” says a friend. “It went from bad to worse.”
In the new issue of PEOPLE, sources share details about Efron’s partying – that sometimes went on for days – and his serious drug problem that included abuse of cocaine and Molly, a form of Ecstasy.
“The partying got out of hand,” says a friend. “He cares so much about his career.”
It’s a bright one, according to Hollywood pals who support the star’s decision to get help.
“The fact that he’s seeking help,” says his Parkland costar Marcia Gay Harden, “only says great things about him.”
For much more detail on Efron’s struggles and why he decided to go to rehab, pick up the latest issue of PEOPLE, on newsstands Friday