Mr Fisher said his sister had written a lot about her drug use and that numerous things she took had been prescribed by doctors for her mental health conditions.
The coroner's office did not immediately respond to HuffPost's request for further details.
The coroner states that Fisher was suffering from sleep aponea, a common condition that causes people to cease breathing while sleeping, for periods of time that can range from a few seconds up to a few minutes.
Fisher, 60, went into cardiac arrest while on a flight to London to Los Angeles on December 23.
She was the daughter of Hollywood couple Debbie Reynolds and Eddie Fisher.
Todd Fisher, Carrie Fisher's brother, confirmed his mother's death to Variety and told the magazine: "She wanted to be with Carrie". "We're not enlightened. There's nothing about this that is enlightening", he said.
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She also suffered from "drug use" and atherosclerotic heart disease, a condition in which fats, cholesterol and other substances build up on the artery walls, the statement said. 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. "They contained me", she said.
"If you want to know what killed her, it's all of it".
Todd Fisher said it was hard to blame doctors who treated his sister because they were trying to help her. They were doing their best to cure a mental disorder.
"Without her drugs, maybe she would have left long ago".
In the 2015 film "Star Wars: The Force Awakens", also known as "Episode VII" of the franchise, she appeared again as Leia, who by then had become an astute military general.