Oh no, Zac, say it isn't so! The heartthrob may have a serious COCAINE problem! How could this Hollywood hottie have sunk so low?

Zac Efron did NOT go to rehab for alcohol abuse, multiple sources tell TMZ he had a serious cocaine addiction.

Zac completed his stint in rehab earlier this year. We're told the problem spiraled out of control during the filming of Seth Rogen's movie "Neighbors," which was shot during a narrow time frame beginning in April.

Read more at TMZ.com HERE!