Zac Efron has opened up to Bear Grylls about his substance abuse past, citing the pressure of living in the public eye.

The Bad Neighbours star appeared in an episode of the British adventurer's show Running Wild with Bear Grylls, in which he spoke about his struggle with drugs and alcohol.

The 26-year-old star went to rehab twice last year to receive treatment.

He said of his experience: "The challenging part was never the work - that was never it. It was sort of the 'in-between work'. The social aspects outside it - I mean, everywhere you go to a certain extent there is press in some form."

He continued: "I mean, whether you're going out to an event, where you're supposed to be out with friends, there will be press there; if you are leaving your house to go to the grocery store, there will be press there. It can be everywhere, and it's, you know, it can be confusing.

"You spend a lot of time in your house going crazy. You know, pretty soon you need a social lubricant."

He added: "Once I needed that, it became to go anywhere. It was getting to the point where I was caring less about the work and waiting more for the weekend, you know what I mean? Where I couldn't wait to go out, you know, and sort of let loose and have fun."