Speaking in her new 'Stay Strong' documentary on MTV, she said: "I cannot tell you that I have not thrown up since treatment. I cannot tell you that I have not cut myself since treatment. I'm not perfect.
"An addiction is an obsession, something that takes over your mind and your every thought. You think that you can't live without it. For me, it was not eating and purging and self-harming.
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Demi - who was also diagnosed with bipolar disorder while in treatment - added that her troubles stemmed from insecurity and feeling she was "living a lie".
She added: "[I was] looking in the mirror and never feeling good enough. I felt like I was living a lie...I was dealing with all this pain, emotionally. And I felt guilt and shame. I decided to take it out on myself. I harmed myself."
Although Demi shot to fame on Disney show 'Sonny with a Chance', she has no immediate plans to return to TV and will instead focus on her music and her fans, who she dubbed the Lovatics.
She said: "If you took away music, I wouldn't have a reason to live.
Every time someone asks me for a picture or an autograph, even if I'm having a bad day and I'm in a bad mood, I remember, 'You're nothing without this person'. They make it special."