During the tough times in treatment, Lovato says it was the thought of her younger sister, Madison, who plays Juanita Solis, the daughter of Gabrielle on "Desperate Housewives," that got her through her darkest hours.
"A picture of my little sister, on my little bulletin board, was one of the main things that kept me going," she said. "I just kept thinking, 'OK, set this example for your little sister.'"
Lovato wanted to set an example -- not only for Madison, but for all the other women fighting the same issues.
"The real reason why I'm sitting down with you," she said, "is to open up the eyes of so many young girls, that it doesn't have to be this way."
Teen singer and actress Demi Lovato sat down with ABC News for her first television interview since leaving treatment for cutting and eating disorders. Watch Lovato share her story with Robin Roberts Friday at 10 p.m. on "20/20" and on "Good Morning America."