Lovato was "taking shots with her friends," the person said, adding, "Demi wasn't like super sloppy or wasted, definitely was drinking though. Her friends were cheering her on when she took a shot."
A second source said they were celebrating her choreographer's birthday at the bar and later continued the party at the singer's house in the Hollywood Hills.
A third source told E! News that Lovato and her inner circle of friends, who travel with her on tour, have been partying hard for the past several months. A fourth source said that Lovato has gone on multiple benders recently and that her Hollywood Hills home has become known as an after-party spot for her and her entourage.
"She had been partying for 12 straight hours and it caught up with her," a fifth source told E! News. "This was going on for a few weeks and the warning signs were there. She slipped up and thought she could handle it. This is obviously a huge wake-up call. Demi doesn't want to die and she's very grateful to be alive. She will be leaving the hospital and heading straight to rehab. Her family has been by her side supporting her and is getting her the help she needs."
The substance or substances that caused Lovato's overdose have not been disclosed.
"It wasn't heroin," the source said, responding to initial reports.