Jeff Lee, spokesman for the Los Angeles Police Department, said the emergency was in the 8000 block of Laurel View Drive in the Laurel Canyon area.
Representatives for Lovato did not respond to requests for comment.
Lovato has been open about her battle with addiction, and has sought treatment in the past.
"The eyewitness tells ET that at one point during the concert, and just before singing the last verse of the her hit song "Sober", Lovato said, "'F**k, I forgot the words' and walked off stage.
"Sober" did not reveal the nature of Lovato's relapse. "I want to be a role model but I'm only human".
It is the same show that Iggy Azalea spoke of with ET earlier this month, when she excitedly revealed that she was opening for Lovato.
What Trump Thinks Of Queen Elizabeth II After Meeting Monarch
Trump did say he admires the queen and found her to be "incredible", "sharp" and "beautiful". It seems like everybody wants me to ", he was quoted in the Mail on Sunday as saying.
She was scheduled to perform in Atlantic City on Thursday, however it is believed that has been cancelled.
Oh hi Guess who's on @BeatShazamFOX tonight at 8/7c?
Selena Gomez's mom, Mandy Teefey, sweetly took to Instagram on July 24 to post a throwback pic and heartbreaking message about Demi Lovato after the singer was hospitalized for an alleged drug overdose. We do not know her condition.
Phil McIntyre, Demi's manager previously insisted Demi speaks openly about her life to "let people in". It breaks my heart that she is going through this. "Our thoughts go out to Demi and her family", the network said.
A source told People that Lovato was "stable" and that the overdose was not heroin-related. "Sending love and healing prayers to her", talk show host Wendy Williams wrote. Lovato called the affair "a awful experience". "Like all of you I am reeling at the news about Demi". "Love you. Not only for your incredible voice, for your incredible music, but for what you stand for and everything you do".
Tyra Banks added, "Addiction is not a choice". He was not aware that her issues were this severe and intense at this time. The terms sat at the top of Twitter's list of trending topics in the hours following the news.