New York (CNN) -- Actor Philip Seymour Hoffman, who was found dead February 2 on the bathroom floor of his New York apartment with a syringe in his left arm, died of acute mixed drug intoxication, including heroin, cocaine, benzodiazepines and amphetamine, the New York medical examiner's office said Friday.
The manner of death was ruled an accident, the medical examiner's office said.
Dr. Sanjay Gupta, CNN's chief medical correspondent, said that as addicts take mixtures of drugs more chronically, they may not necessarily feel the effects of the narcotics, which still suppress the respiratory system.
"They're not feeling it, but it's still having an impact on their ability to breathe, and that's the real problem," he said. "It's called stacking. You can stack the same drug too close together, or you can start to stack other drugs, one on top of the other. That's how people get into trouble. They do call it accidental death as well."
Police found nearly 50 envelopes branded "Ace of Spades" filled with what they believe was heroin in the actor's Manhattan apartment, two law enforcement sources familiar with the inquiry said.
Used syringes, prescription drugs and empty bags that authorities suspect were used to hold heroin also were found in the apartment where Hoffman, 46, was found dead, sources said.
He was expected to pick up his children that day but didn't show up, the official said. Playwright David Katz and another person went to the apartment and found him dead, the official said.
Police officers found him in a T-shirt and shorts with his eyeglasses still on his head.
Police also found several empty bags branded "Ace of Hearts" -- a street name for heroin -- in the apartment, law enforcement sources familiar with the investigation told CNN.