Demi Lovato is "stable" and recovering in hospital in Los Angeles after being found unconscious at her Hollywood Hills home allegedly as the result of an overdose.

TMZ first reported that the singer was transported to an undisclosed medical facility shortly before noon on Tuesday (local time) after friends called 911.

A law enforcement source confirmed she was given Narcan when she was found, a medication that's used to try and reverse an opioid overdose, the Daily Mail reports.

While it's been speculated that Lovato overdosed on heroin, TMZ later reported that the star had refused to disclose to paramedics what she had taken and that no drugs were found at her home.

A source told the website that she had not overdosed on heroin but wouldn't disclose any further details. However, the songstress has previously struggled with cocaine and Oxycontin addictions.

According to UsWeekly, the Narcan was kept on hand by one of the singer's friends "in case something like this happened."

"Her friends knew this was coming because she's been using so much again. They were up all night partying the night before at her house," a source told UsWeekly. "Luckily, the Narcan worked and she will recover."

Law enforcement told TMZ that there is currently no criminal investigation because they could not determine what drug Lovato was under the influence of.

It's reported that the Confident singer's mother Dianna De La Garza is at her bedside.

Demi's aunt, Kerissa Dunn, posted on social media Tuesday afternoon that the 25-year-old is "awake and responsive", TMZ reported, and also asked fans to pray for the hitmaker. However, it seems the posts have since been deleted.

Following the update, Demi's rep said in a statement to Variety: "Demi is awake and with her family who want to express thanks to everyone for the love, prayers, and support.

"Some of the information being reported is incorrect and they respectfully ask for privacy and not speculation as her health and recovery is the most important thing right now."

Meanwhile, Fox announced it is replacing Tuesday's scheduled episode of Beat Shazam in which Demi appears due to the day's events. She had tweeted about her appearance on the show just hours before she was rushed to the hospital.

The singer's Thursday concert in Atlantic City, New Jersey, has also been cancelled, as Variety confirmed.

Lovato has been incredibly open about her struggles with alcohol and drugs, and earlier this year debuted her single Sober in which she detailed her battles and path to recovery.

She performed that song on Sunday night at the California Mid-State Fair, her last appearance before being hospitalised.

During the performance, Lovato struggled to remember the words to her song.

Demi got candid about her drug struggles in the YouTube documentary Simply Complicated, which was released last year.

In that documentary Lovato said that she tried cocaine at 17, right around the time she was shooting to fame on the Disney show Sonny With A Chance.

"I loved it. I felt out of control with the coke the first time that I did it," explained Lovato.

She also spoke about how addiction ran in her family, and her mother's attempts to keep her daughter away from drugs.

"My dad was an addict and an alcoholic," explained Lovato.

"I guess I always searched for what he found in drugs and alcohol because it fulfilled him and he chose that over a family."

It was while on tour with the Jonas Brothers that Lovato said her problem got out of control, resulting in one period where she used drugs ever day for two months.

At 18, she checked into rehab for the first time.

She said she felt great after leaving rehab, but soon found herself relapsing on drugs.

"I wasn't working my program. I wasn't ready to get sober. I was sneaking it on planes, sneaking it in bathrooms, sneaking it throughout the night," said Lovato.

"Nobody knew."

She even gave interviews about her new sober lifestyle while high on drugs she said, while cycling through sober companions.

"I was using while I had a sober companion, and I went through like 20 sober companions. I was either craving drugs or on drugs," explained Lovato.

"I was not easy to work with. It's embarrassing to look back at the person I was."

One night, she mixed cocaine and Xanax she said, in what was almost a fatal mistake.

"I started to choke a little bit, and my heart started racing. I remember thinking, 'Oh my God, I might be overdosing right now'", said Lovato.

Her low point came in 2012 when she partied all night with strangers in a hotel and threw up on the way to her American Idol appearance.

That is when her management team informed her that if she did not get sober they would no longer keep her as a client.

For the next six years Lovato stayed clean as her career thrived, though she admitted to dealing with other problems like an ongoing eating disorder.

That came back in a big way in 2016 she said after her split for Wilmer Valderama, with the singer saying that being alone triggers the disorder.

"When I was in a relationship with Wilmer I went three years without purging, and when we broke up, that's one of the first things I did," said Lovato.

"The less I have to think about food, the easier it is to go about having a normal life, and I don't want to let anybody down, so when I do have moments when I slip up, I feel very ashamed.

"What started the relapse was missing Wilmer. When I feel lonely my heart feels hungry and I end up binging."

She also hints in her song Sober that she recently relapsed, and has been candid about her struggles with mental health as well over the years.

"The last decade has taught me a lifetime of lessons," said Lovato towards the end of the documentary.

"I've learned that secrets make you sick. I'm learning how to be a voice and not a victim. I've learned sex is natural. I've learned that love is necessary, heartbreak is unavoidable and loneliness is brutal.

"I've learned that the key to being happy is to tell your truth and be OK without all the answers."

If you or someone you love is struggling with addiction issues and needs support please contact the Alcohol Drug Helpline on 0800787797.