News of Demi Lovato's apparent overdose has rocked Hollywood, leaving fans with more questions than answers. Here, E! News takes a deeper look at the superstar's hospitalization.

A spokesperson for the Los Angeles Fire Department told E! News Tuesday they "transported a 25-year-old female patient to a local hospital," while the Los Angeles Police Department confirmed both divisions had "responded to a medical emergency" near her Hollywood Hills home; NBC News reported Lovato was taken from her home to Cedars Sinai Medical Center.

(For privacy reasons, the LAFD and LAPD would not reveal the woman's identity.)

First responders who were called to the "Sorry Not Sorry" singer's home used naloxone, an opioid-overdose antidote, to reverse the effects of the overdose, multiple sources told NBC News. TMZ originally reported she had overdosed on heroin, but then backtracked, saying it was another drug; a source close to Lovato told E! News the singer did not overdose on heroin. Audio of the emergency call, obtained by TMZ, revealed she was unconscious upon their arrival. Lovato allegedly refused to tell police and first responders what drugs had caused her overdose, according to The Blast; LAPD officers collected an "item of evidence" related to illegal drugs that are not typically associated with heroin, the website claimed. A spokesperson for the LAPD later confirmed to E! News Lovato is not under any form of criminal investigation.