The Neighbors actor, 26, was the first celebrity to be featured in the reality series where Grylls takes celebrities on two-day excursions around the "wildest and most remote locations in the U.S. and around the world."
"The challenging part was never the work. It was sort of the in between work. The social aspects of it," Efron said when asked what prompted him to fall into addiction.
"I mean everywhere you go to a certain extent there is press at some point," he continued, explaining that he not only encounters photographers at events, but also while doing regular activities like hanging out with friends and going to the grocery store.
"It can be confusing. You spend a lot of time in your house going crazy," Efron said. "You know pretty soon you need a social lubricant and once I needed that it became to go anywhere. I was getting to the point where I was caring less about the work and waiting more for the weekend when I couldn't wait to go out."
The High School Musical star went on to say that he never wants to be in a situation where he needs to take anything from the outside to feel good on the inside.
"That takes a lot of work. Is just meditation and slowing down your brain," he said.
Sources revealed that Efron secretly completed two stints in rehab -- supposedly for molly and cocaine -- in September 2013. The actor opened up about his addiction in April of this year, telling The Hollywood Reporter that addiction is "a never-ending struggle."