Traces of heroin and MDMA, popularly known as ecstasy, were also found in the Star Wars actress's system.
But investigators could not determine what impact the cocaine and other drugs had on her death.
The findings were based on toxicology samples taken when Fisher arrived at a Los Angeles hospital.
Investigators could not say when the actress had taken the MDMA or heroin.
The star, who played Princess Leia in the film series, died on 27 December.
'Social stigmas'
On Friday, a statement from the Los Angeles coroner said the exact cause of death was unknown but cited factors including sleep apnoea, heart disease and drug use.
Sleep apnoea is a common condition in which a person stops breathing during sleep, either for a few seconds or minutes.
In a statement released to People magazine after the coroner's ruling, Fisher's daughter Billie Lourd said: "My mum battled drug addiction and mental illness her entire life. She ultimately died of it.
"She was purposefully open in all of her work about the social stigmas surrounding these diseases."
Her manner of death will be listed as undetermined, the coroner's statement said.
Fisher's death certificate, issued in January, stated that the cause of death was "cardiac arrest/deferred".
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