"We are listing that he abused cocaine and that's what resulted in the cocaine toxicity," said an official at the San Diego County medical examiner's office.
Cardiovascular disease and pulmonary emphysema were also given as "significant" factors in the death.
Turner's daughter Mia said she was shocked by the report.
The singer had waged an "ongoing struggle" with drugs, she said, but the coroner was "overstating the situation".
"Daddy at that point was not doing drugs to the level it leads to believe," she told the North County Times in a telephone interview.
The former husband of Tina Turner died at his home near San Diego on 12 December.
Paul Parker, chief investigator at the medical examiner's office, was quoted by The Associated Press as saying hypertensive cardiovascular disease and pulmonary emphysema were also "significant and contributing factors" in Turner's death.
Rising to fame in the 1960s, the musician is best remembered for his musical partnership with Tina.
Their stormy marriage, in which she said he abused her, overshadowed his considerable achievements in popular music.