Fisher, 60, was taken to the hospital by Los Angeles Fire Department paramedics in December after falling ill during her 11-hour flight from London to Los Angeles International Airport.
The sleeping condition and a build-up of fatty tissue in her arteries were among the issues recorded, a Los Angeles coroner said on Friday.
He said his sister wrote about her drug use frequently, and numerous drugs she took were prescribed by doctors to treat her mental health conditions.
No more information was released by the coroner, nor were questions answered about whether a full post-mortem examination report and toxicology results were available.
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The pair were laid to rest together in a cemetery in Hollywood Hills.
It also said: "How Injury Occurred: Multiple drug intake, significance not ascertained". She noted in other interviews that she had used cocaine on the set of "The Empire Strikes Back", and struggled with addictions to prescription medication.
"If you want to know what killed her, it's all of it. Can you really blame them?" he said. The statement also mentions drug use but doesn't specify which drugs or how long ago they were taken. As well as the Star Wars films, she appeared in Austin Powers, The Blues Brothers, Charlie's Angels, Hannah and Her Sisters, Scream 3 and When Harry Met Sally.
"Star Wars" star Carrie Fisher's mother was a famous actress, singer and dancer.