Demi Lovato: 'I was a nightmare to work with'

Singer Demi Lovato was unable to go an hour without cocaine at the height of her addiction.

The Cool for the Summer star battled alcohol and drug abuse as a teenager and in a candid new interview with Refinery29, Demi revealed she would ignore her parents' best attempts to keep her on the straight and narrow by reminding them she was paying their bills.

"Prior to getting sober, I was one of those people who was like, I don't give a f**k, whatever," she said, "and I used that as an excuse to do whatever I wanted. I was a nightmare to work with."

The 23-year-old celebrated four years of sobriety earlier this year (16), but her efforts to change her lifestyle and behaviour haven't come easy.

"I had to learn the hard way that I can't do parties anymore," she continued. "Some people can go out and not be triggered, but that's not the case for me."

Despite her four-year milestone, the singer knows there are still detractors out there who are waiting for her to mess up.

"I'm still underestimated… I still have more things to prove - not just about the things I can do with my voice," she said. "Some people think that because I'm young, I can't stay sober. But these are things I want to prove to myself."

Demi prides herself on being honest about her past demons with her loved ones and loyal fans, adding: "I'd rather live my life free and open than closed off, where people like me for something that I'm not."