Sources said that after ascending to A-list status following the success of the second High School Musical film, he fell in with the wrong crowd.
Zac is said to have beaten his demons, even avoiding alcohol, after a second visit to rehab was prompted by a relapse while shooting the Seth Rogen comedy, Neighbours.
Later in September, Zac broke his silence for the first time since news of his attempt to get help became public knowledge.
Posting an Instagram picture of himself at the Machu Picchu mouton ruins in Peru, he wrote in the caption, "Hey guys! Just returned from an incredible trip to Peru with my dad and wanted to thank you all for your support these past few weeks… means the world to me. Love you guys — Z."