Carter, 34, the younger brother of Backstreet Boys singer Nick Carter, was found dead at his home in Lancaster, California, on November 5.
Now that the autopsy is done, we know that he drowned because of the sedatives he had taken and the gas he had breathed in.
Alprazolam, which is often sold as Xanax, was found in his body.
Difluoroethane, a gas that is squeezed, was also found.
The story says that it is a "commonly used propellant in air spray cleaners" that "can make you feel happy when you breathe it in."
Investigators found prescription bottles and cans of an electric duster that he had used to inhale.