According to the Los Angeles Coroner's Office, contributing factors of Houston's death were a heart condition and cocaine use. The singer's heart condition caused blockages in her arteries, according to the coroner's report.
"We are saddened to learn of the toxicology results, although we are glad to now have closure," said Patricia Houston, the singer's sister-in-law and manager.
Coroner's spokesman Craig Harvey said the results indicated Houston was a chronic cocaine user.
"We feel that the cocaine, coupled with the Atherosclerotic heart disease, complicated her condition as such so that if she did have, for instance a cardiac event, all of that combined, resulted in her drowning. Chances are, had she not had the pre-existing heart disease and cocaine use, she may not have drowned," Harvey said.
Houston, 48, was found dead on Feb. 11, submerged in a hotel bathtub filled with water, just one day before the Grammys.
Marijuana, Xanax, Flexeril and Benadryl were also found in her system, but they did not contribute to her death, the coroner's report said. The findings noted that the death was ruled accidental, and trauma or foul play was not suspected.
Several bottles of prescription medications were found in her hotel room at the time of her death, but coroner's officials said they weren't in excessive quantities. The full autopsy report will be released in about two weeks, officials said.
The Associated Press contributed to this story.