It came as a shock when Zac Efron entered rehab last year.

The former Disney Channel star is one celebrity joining Bear Grylls for "Running Wild with Bear Grylls," and during their adventure, Efron opened up about his addiction, according to the Detroit Free Press.

"The challenging part was never the work," he said. "That was never it. It was sort of the in-between work -- the social aspects outside of it. I mean, everywhere you go to a certain extent, there is press in some form. Whether you're going to an event where you're supposed to be out ... there will be press there, if you're leaving your house to go to the grocery store, there will be press there. It can be everywhere and it can be confusing. You spend a lot of time in your house, going crazy and pretty soon you need a social lubricant."

Efron said that soon the weekend was all he was waiting for, and he eventually realized work was taking a backseat.

"But then when Monday and Tuesday were difficult to get through, I was like, 'Oh this is bad,'" he said. "I just really want to never again have to take anything from the outside into me to feel good about my outside, to be comfortable in my present skin."

Earlier this year, sources said that Efron had changed his life after rehab, according to People.

He cut out people who were only into partying, and he was taking his sobriety very seriously. He was seen wearing a six-month sobriety chip at a Lakers game in December 2013.

The actor also said that he was now "completely sober."

He added that his parents, roommates and friends were "stoked" about the changes.

"The people I work with, the people I really care about are so much happier," he said. "And I feel so much better..."