The announcement Thursday ends weeks of speculation about what killed the Grammy-winning singer on Feb. 11.
Houston was found submerged in the bathtub of her room at the Beverly Hilton Hotel on the eve of the Grammy Awards.
Several bottles of prescription medications were found in her hotel room, but coroner's officials said they weren't in excessive quantities.
Coroner's spokesman Craig Harvey says cocaine metabolites were found in Houston's system, and it was listed as a contributing factor in her death. He says the results indicated Houston was a chronic cocaine user.