"I never found out until I went into treatment that I was bipolar," the 18-year-old actress and singer told People. "Looking back it makes sense. There were times when I was so manic, I was writing seven songs in one night and I'd be up until 5:30 in the morning."
Lovato, who said she has battled depression "from a very young age," originally sought treatment for bulimia, anorexia and cutting, according to the magazine.
"I feel like I am in control now where my whole life I wasn't in control," she said.
Lovato tweeted her support for fellow actress Catherine Zeta-Jones shortly after she came forward with her own recent bipolar II diagnosis. " I don't know Catherine Zeta-Jones personally but what she has decided to do [it's] SO brave," she wrote. "And SO difficult but worth it... I'm proud of her."
Lovato also recently announced her decision to leave her Disney channel series, Sonny with a Chance, in order to focus on her music.