Lovato had apparently been out on Monday night celebrating a friend's birthday.
The Disney star has battled substance abuse for years and spent some time in rebab in 2010.
In March she had celebrated six years of sobriety.
Last month she released her new single Sober where she suggested she'd fallen off the wagon.
The lyrics allude to her having relapsed from sobriety.
"Mama, I'm so sorry I'm not sober anymore / And Daddy, please forgive me for the drinks spilled on the floor.
"To the ones who never left me / We've been down this road before / I'm so sorry, I'm not sober anymore."
In YouTube documentary Simply Complicated, which was released last month, Lovato opened up about her drug struggles.
She spoke of trying cocaine at 17, right around the time she was shooting to fame on Disney show Sonny With a Chance.
"I loved it. I felt out of control with the coke the first time I did it," she said.
Lovato said her dad was an alcoholic and addict ad her mother tried to keep her away from that life.
"I guess I always searched for what he found in drugs and alcohol because it fulfilled him and he chose that over family," she told the documentary.
She checked into rehab for the first time at 18 but relapsed soon after leaving.
No one knew the star had fallen off the waggon and she even gave interviews about her new sober life while high on drugs.
Celebrities send messages of love and support
Celebrtities have taken to social media to share their messages of support to Lovato.
