Coroner's spokesman Craig Harvey said drug tests indicated the 48-year-old US singer was a chronic cocaine user.
The announcement ends weeks of speculation over the cause of Houston's death.
She was found submerged in the bath of her Los Angeles hotel room on the eve of the Grammy Awards on 11 February.
In a statement, the LA County Coroner's office described Houston's manner of death as an "accident", adding that "no trauma or foul play is suspected".
The cause was cited as drowning and "effects of atherosclerotic heart disease and cocaine use".
Other drugs found in her blood included marijuana, as well as an anti-anxiety drug, a muscle relaxant and an allergy medication.
But these were not factors in her death, the coroner's statement said.
Patricia Houston, the singer's sister-in-law and manager, told the Associated Press news agency: "We are saddened to learn of the toxicology results, although we are glad to now have closure."
The pop star was laid to rest at a cemetery in her home state of New Jersey after a funeral that was attended by celebrities including Oprah Winfrey, Alicia Keys, Mariah Carey and Mary J Blige.
The singer, who was one of the world's best selling artists from the mid-1980s to late 1990s, had a long battle with drug addiction.