Telling the publication that at her lowest point, she was unable to go an hour without cocaine, she would resist her parents' discipline by saying, "Try to ground me — I pay your bills."
"Prior to getting sober, I was one of those people who was like, I don’t give a f**k, whatever," she adds. "And I used that as an excuse to do whatever I wanted. I was a nightmare to work with."
Lovato celebrated four years of sobriety in March, telling ET that when it comes to staying clean, "I think what inspires me is remembering that I deserve to be the best that I can be and also knowing people look at me as a role model - it gives me the fire to continue to be strong."
Of course, sobriety is a lifelong battle, and Lovato tells the publication that she had to resist the urge to watch the Oscar-winning documentary Amy, about the troubled life of late singer Amy Winehouse.
"To see white powder in a movie.... To see someone shooting up?" she says. "It’s too triggering. If I feel even 1% unsure that I’m in a place where I can watch it, then I just don’t do it."
And Demi understands that even through all of her positive strides, she still has her detractors.
"I’m still underestimated… I still have more things to prove – not just about the things I can do with my voice," she says. "Some people think that because I’m young, I can’t stay sober. But these are things I want to prove to myself."
Apart from sobriety, Lovato addresses a number of things in the interview, including her relationship with Wilmer Valderrama. While the singer said last year she would say "Yes" if her boyfriend ever proposed, the couple is keeping those details to themselves, for now.
"It’s nobody’s business but ours, and when it happens, it happens," she says.
"There’s way too much shame put on victims coming forward talking about being date-raped, raped, sexually abused," she tells the magazine. "So then people feel like they can’t come forward anymore because they’ll just be torn to shreds.”
To Lovato, support of other women is a critical element to feminism.
"My thing is, don’t brand yourself a feminist if you don’t do the work," she says. "I have an immense amount of respect for women like Lena Dunham… or Beyoncé, who make amazing political statements through their work.”