American celebrity gossip website TMZ reported on Tuesday the American singer, 25, was taken ill following a suspected overdose at her home in the Hollywood hills.
A Los Angeles Police Department spokesman told the Press Association the force was called to an address in Hollywood at around 11am local time.
They said the patient, a 25-year-old female, was in the process of being taken to hospital when they arrived and is in a stable condition.
Police cannot confirm the identity of the patient, the spokesman said.
Following the reports, US chatshow host Ellen DeGeneres tweeted: “I love @DDLovato so much. It breaks my heart that she is going through this. She is a light in this world, and I am sending my love to her and her family.”
And Lovato’s fellow singer Ariana Grande posted: “I love u @ddlovato.”
In June Lovato, who has been open about her battle with alcohol and substance abuse in the past, released a single suggesting she had suffered a setback in her recovery from addiction.
The singer referred to a relapse on her latest track, titled Sober, which came after she celebrated six years of sobriety in March.
In June she was forced to cancel two UK shows due to illness.
Lovato called off concerts in London and Birmingham after suffering from swollen vocal cords.