The celebrity news website reports police told them the 25-year-old was taken to an LA hospital from her Hollywood home but her condition is unknown.
The American singer was reportedly treated with Narcan – an emergency treatment for narcotic overdoses.
Paramedics found her unconscious when they arrived at her home.
The singer, who has struggled with substance abuse for some years, released a song recently called Sober, in which she reveals she had relapsed after she celebrated six years of sobriety in March.
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.”
Ariana Grande posted: “I love u @ddlovato.”
The singer has been open about her addictions and her struggle with bipolar disorder and an eating disorder.
She has spent time in rehab and has admitted self-harming.
The Let It Go singer has worked with charities in the US to raise awareness of mental illness.
A spokesman for the Los Angeles fire department said they received a call at 11.22am for a “medical emergency” and took a 25-year-old woman from a property in Hollywood to a local hospital.