The cause of Carrie Fisher's death has been released.

Six months on from her death, an official from the Los Angeles County coroner’s office has announced Carrie Fisher died from sleep apnea and a combination of other factors but added investigators were not able to pinpoint an exact cause.

According to the statement, among the factors that contributed to Fisher’s death was buildup of fatty tissue in the walls of her arteries, the office said in a news release on late Friday.

The release states that the Star Wars actor showed signs of having taken multiple drugs, but investigators could not determine whether or not they contributed to her death on December 27.

Her manner of death would be listed as undetermined, the agency said.

The agency did not immediately respond to a request for additional details about whether a full autopsy report and toxicology results were available.

Sleep apnea is a condition in which a person's breathing pauses during sleep, with pauses lasting anywhere from seconds to several minutes.

60-year-old Fisher suffered a medical emergency on December 23 when flying from London to Los Angeles. Four days, later, she was pronounced dead. Her mother, longtime movie star Debbie Reynolds, died the following day.

The actresses were laid to rest together at Forest Lawn-Hollywood Hills, a cemetery where numerous celebrities are buried.

Fisher's brother, Todd Fisher, said he was not surprised by the results. He added that his family did not want a coroner's investigation of his sister's death. "We're not enlightened. There's nothing about this that is enlightening," he said.

"I would tell you, from my perspective that there's certainly no news that Carrie did drugs," Todd Fisher said. He noted that his sister wrote extensively about her drug use and that many of the drugs she took were prescribed by doctors to try to treat her mental health conditions.

Fisher long battled drug addiction and mental illness. She said she smoked pot at 13, used LSD by 21 and was diagnosed as bipolar at 24. She was treated with electroshock therapy and medication.

"I am not shocked that part of her health was affected by drugs," Todd Fisher said.

He said his sister's heart condition was probably worsened by her smoking habit, as well as the medications she took. "If you want to know what killed her, it's all of it," he said.

Todd Fisher said it was difficult to blame doctors who treated his sister because they were trying to help her.

"They were doing their best to cure a mental disorder. Can you really blame them?" Fisher said. "Without her drugs, maybe she would have left long ago."

Carrie Fisher made her feature film debut opposite Warren Beatty in the 1975 hit Shampoo. She also appeared in Austin Powers, The Blues Brothers, Charlie's Angels, Hannah and Her Sisters, Scream 3 and When Harry Met Sally.

She will reprise her role as Leia Organa in the eighth instalment of the core Star Wars franchise, The Last Jedi, which will be released in December.