It shocked the world when it was revealed that clean cut star Zac Efron completed rehab for alcohol and cocaine addictions, but what's more shocking is that he actually went to rehab twice ... and it was bad.

TMZ reports that Efron had been using cocaine for more than two years while also dabbling in Molly, a pure form of ecstasy.

How did Efron, who had a squeaky clean rep since bursting onto the scene with 'High School Musical,' get into drugs? Sources close to the actor point to four reasons for his drug dabbling, which soon escalated into a full-blown addiction.

One reason is Efron's relationship with his parents, who, despite him being 25, allegedly still want to control his life and career. Another is Efron's movie career in itself, which he feels has stalled somewhat post-'HSM,' despite star turns in 'Hairspray' and 'The Lorax.' Other factors are "girl problems" (which sources say have nothing to do with ex Vanessa Hudgens) and falling into a bad group of pals.

In an effort to get clean, Efron left California in March of this year for an intense outpatient residence where he stayed for several weeks.

However, when filming 'Neighbors' with Seth Rogen in April, Efron relapsed hard. He reportedly missed several days of filming because he wasn't showing up and it was common knowledge on set that he was using cocaine again.

Once filming wrapped, Efron got more outpatient care, which he completed. Here's hoping he has a steady and permanent recovery!

More From StarCrush