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 in a statement.
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.
Robert Vineberg, a 57-year-old musician, was arrested in connection with Hoffman's death and released on bail earlier this month. Vineberg was among four people arrested in Manhattan in the days after Hoffman's death.
Prosecutors said Vineberg, who was arrested on a felony charge of criminal possession of a controlled substance, had just under 50 small bags of heroin as well as packaging paraphernalia in his apartment during a raid. In another one of his apartments in the same Mott Street building, prosecutors said, 250 small bags of heroin were found.
Vineberg was found to have the actor's phone number stored in his cell phone, a law enforcement official told CNN.
Two other people arrested in connection with Hoffman's death -- Juliana Luchkiw and Max Rosenblum, both 22 -- were released earlier this month until their next court dates.
Prosecutors did not file charges against a fourth person arrested in the raid.
Hoffman was mourned in New York February 7 in a star-studded private funeral attended by family and close friends.
Hoffman, who was nominated for Academy Awards four times, won the Oscar for best actor in 2006 for his portrayal of writer Truman Capote in "Capote." He earned Academy Award nominations for roles in "Charlie Wilson's War," "Doubt," and "The Master."