The father of Hollywood actor Heath Ledger issued a warning to users of prescription drugs after a coroner confirmed the Brokeback Mountain star had died of an accidental overdose.

In a statement released through his son's publicist, Ledger’s father, Kim, said: “Heath’s accidental death serves as a caution to the hidden dangers of combining prescription medication, even at low dosage.”

His comments came minutes after New York's chief medical officer, Charles Hirsch, confirmed the cause of death.

“Mr Ledger died as the result of acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam, and doxylamine," said Hirsch. "We have concluded that the manner of death is accident, resulting from the abuse of prescription medications."

There has been much speculation surrounding the sudden death of the 28-year-old Australian, best known for his portrayal of a gay cowboy in Brokeback Mountain, who was found dead in his Manhattan apartment on January 22.

Ledger’s housekeeper discovered his body on his bed with prescription sleeping pills, painkillers and anti-anxiety medicine nearby.

An initial post-mortem was deemed inconclusive and there has been conflicting speculation surrounding drug use and that he was suffering from insomnia and pneumonia.

The autopsy report came as Ledger’s family – his father Kim, mother Sally, sister Kate, his ex-fiancée Michelle Williams and their daughter Matilda – returned to his home town of Perth, Australia, to attend a private funeral for the actor.

Williams and Matilda, two, who was clutching a white stuffed rabbit, were escorted through Perth airport by security. Last week Williams, who split with Ledger in September, released a statement in which she said: “my heart is broken”.

"His family and I watch Matilda as she whispers to trees, hugs animals, and takes steps two at a time, and we know that he is with us still. She will be brought up in the best memories of him," she said.

Ledger’s family had spent more than a week in the US where they had attended memorial services for the popular actor, including an intimate ceremony in Los Angeles for his immediate family and close friends, including Williams and Naomi Watts, the Australian actress and another long-term ex-girlfriend.

On Saturday a service for his friends and colleagues was held on a Sony lot in Los Angeles where Tom Cruise and Katie Holmes, Sienna Miller, Ellen Degeneres and Todd Haynes, who directed Ledger in I’m Not There, gathered to remember him.

Shortly after he died Ledger’s family released a statement saying his death was a “very tragic, untimely and accidental passing”.

"Heath has touched so many people on so many different levels during his short life, but few had the pleasure to truly know him’” the Ledger family said in a statement.

The actor’s performance in the critically acclaimed Brokeback Mountain earned him an Oscar nomination in 2006. A week before his death he was in London filming Terry Gilliam’s The Imaginarium of Doctor Parnarssus, which has since been postponed, while his last starring role, as the Joker in the Batman film The Dark Knight, is set for release later this year.

A private funeral is expected to take place in Perth on Saturday.

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