Actor Heath Ledger died from an accidental overdose of a deadly cocktail of prescription drugs including powerful painkillers, sleeping pills and anti-anxiety medication, the New York City medical examiner's office has ruled.

"Mr. Heath Ledger died as the result of acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine," said medical examiner spokeswoman Ellen Borakove in a statement on Wednesday.

The drugs listed by Borakove are the generic versions of OxyContin, a time-release painkiller related to morphine, anti-anxiety drugs Valium and Xanax, and sleeping pills Restoril and Unisom. Hydrocodone is another name for the opioid Vicodin.

The release did not go into details of the concentrations of each drug found in his system, nor did it say whether some were more influential than others in causing his death. Borakove simply said it was the "cumulative effects" of the drugs combined.

In a statement released Wednesday through Ledger's publicist, his father Kim warned others of the dangers of mixing prescription pills.

"While no medications were taken in excess, we learned today the combination of doctor-prescribed drugs proved lethal for our boy," he said. "Heath's accidental death serves as a caution to the hidden dangers of combining prescription medication, even at low dosage."

An Oscar nominee, Ledger was highly revered among his colleagues and fans for his portrayal of a gay cowboy in "Brokeback Mountain."

He had just completed the role of the Joker in the upcoming Batman film, "The Dark Knight," and Bob Dylan in "I'm Not There," and had told the media that his immersion into the roles had made it difficult to sleep.

"Last week I probably slept an average of two hours a night," he had said in the weeks before his death, adding that even after two Ambien sleeping pills he could only manage to sleep for an hour. "I couldn't stop thinking. My body was exhausted, and my mind was still going."

His most recent project was the $30 million Terry Gilliam film "The Imaginarium of Doctor Parnassus."  He had just returned from working on the film in London when he died.

Ledger was found dead in his New York City rental apartment on Jan. 22, surrounded by six types of prescription pills. The 28-year-old had been awaiting the arrival of a masseuse, who found him face down on his bed and proceeded to call Mary-Kate Olsen three times before dialing 911.

The family of the Australian actor has spent the past few days mourning together in their hometown of Perth following the return of his parents, who spent two weeks in the United States following Ledger's death. They are reportedly planning a private service in their city.

With files from the Associated Press