Demi Lovato felt like she was "in prison" initially when she entered rehab.

The 20-year-old singer and US The X Factor judge sought help at a Chicago treatment facility in late 2010 for bulimia and self-harm issues.

Demi admits that she struggled at the beginning of the programme.

"Treatment was so difficult at first, I remember walking around saying 'I'm in prison!' They needed to have those strict rules in order for me to understand how sick I was," Demi revealed in an interview with Katie Couric that airs Monday.

"I wasn't allowed to use the bathroom by myself. We had specific phone times. There are tons of things you weren't allowed to have, you weren't allowed to have certain hair products or whatever that you could injure yourself with or possibly drink and you were just stripped of a lot of things.

"I also had somebody watching over me every single time I ate. And if I didn't finish what was on my plate, and often times I would cry because I physically couldn't stomach it and if that happened I would have to have little consequences, nothing horrible just not being able to go to the cafeteria to eat."