Houston, 48, was found dead in the bathtub of her Beverly Hills hotel room on February 12, the night before the Grammy Awards.
Harvey said toxicology tests also turned up marijuana, an anti-anxiety medication, a muscle relaxant and anti-histamine in Houston's system but found that they did not contribute to her death.
No trauma or foul play were suspected in the entertainer's death, the coroner's office said.
Houston, known for a number of hit songs including "I Will Always Love You," had long battled addictions to drugs, including cocaine.
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