Carrie Fisher's Cause of Death Revealed: Actress Died of Sleep Apnea and 'Other Undetermined Factors'

The actress' daughter, Billie Lourd, tells ET that she hopes her mom's death will 'encourage people to be open about their struggles.'

Carrie Fisher's cause of death has been revealed.

Nearly six months after the actress' death, the L.A. County Medical Examiner's office confirms to ET that Fisher died of sleep apnea and other undetermined factors.

WATCH: Carrie Fisher's Death Certificate Lists Cause of Death But Questions Still Remain

Fisher died on Dec. 27, 2016, after going into cardiac arrest on a flight from London to Los Angeles on Dec. 22. She was 60. The Medical Examiner's office revealed on Friday that other conditions leading to the Star Wars actress' death were atherosclerotic heart disease and drug use.

According to the press release, Fisher's cardiac arrest was caused by multiple drug intake, with "significance not ascertained." The manner of Fisher's death has been ruled undetermined.

"My mom battled drug addiction and mental illness her entire life. She ultimately died of it," Fisher's daughter, Billie Lourd, said in a statement to ET. "She was purposefully open in all of her work about the social stigmas surrounding these diseases."

"She talked about the shame that torments people and their families confronted by these diseases. I know my Mom, she’d want her death to encourage people to be open about their struggles," Lourd continued. "Seek help, fight for government funding for mental health programs. Shame and those social stigmas are the enemies of progress to solutions and ultimately a cure. Love you Momby."

Fisher's death certificate was released in January, listing "cardiac arrest/deferred" as the cause of death. 

WATCH: Carrie Fisher's 'Star Wars' Family Remembers Her 'Vibrant' Legacy: 'She Lived Her Life the Way She Wanted To'

Six months after her death, Fisher is still being remembered by family, friends and fans. See Mark Hamill's touching tribute to the actress during Sunday's Tony Awards' In Memoriam segment in the video below.