Updated: 2008-02-07 09:56

The actor Heath Ledger died from an accidental overdose of six different drugs — painkillers and sedatives — the medical examiner said Wednesday, leading doctors to warn of the dangers of mixing prescription drugs.

The 28-year-old film star died "of acute intoxication" from the combination of two strong painkillers, two anti-anxiety medicines and two sleeping aids, according to the medical examiner's office.

Among the drugs found in his body were oxycodone, a painkiller sold as OxyContin and used in other pain relievers such as Percodan and Percocet. Others included drugs sold as anti-anxiety pills Valium and Xanax, which are sedatives.

The medical examiner and police wouldn't identify the medications Ledger had in his apartment when his body was discovered on Jan. 22, nor would they discuss who had prescribed them. It also wasn't known why he had the drugs; he said in a newspaper interview last year that he needed sleeping pills after two stressful acting jobs.

The Drug Enforcement Administration is investigating how Ledger got the medications. It's common for investigators to review prescriptions when so many drugs are involved in an overdose death, said spokesman Rusty Payne.

Doctors not connected with the case said it would be unlikely for one doctor to order all the drugs. However, they said it's not unusual for people to be prescribed both painkillers and sedatives, and overdoses are not uncommon.

"This is not rock star wretched excess," said Cindy Kuhn, a pharmacology professor at Duke University. "This is a situation that could happen to plenty of people with prescriptions for these kind of drugs."

Kuhn said some of the drugs are long-lasting and Ledger could have taken them over a period of several days. The medical examiner's office wouldn't say what concentrations of each drug were found in Ledger's blood.

"What you're looking at here is the cumulative effects of these medications together," said the spokeswoman, Ellen Borakove.

Police had said they found six bottles of anti-anxiety medicines, sleeping pills and other medicine in his Manhattan apartment after the Oscar-nominated actor was discovered dead in his bed last month.

"This was not a deliberate attempt to kill himself. This was an accident," said Lawrence Kobilinsky, head of forensic science at John Jay College in New York. He had no role in the investigation. "He just took too many drugs having similar effects on the central nervous system."

Experts said the combination of sedatives and the other medicines likely combined to suppress his brain function and his breathing. They said that Ledger probably had been prescribed the medicine by a number of different doctors, because several of them were from the same class of drugs and used to treat similar symptoms.

"It doesn't make sense" that one doctor would prescribe all those, said Dr. William Lee, an internal medicine specialist at the University of Texas-Southwestern in Dallas. "It's more likely that he got them from different prescribers."

Jane Prosser, a medical toxicologist from New York University School of Medicine, said patients can often end up with similar medications prescribed by different doctors, who are unaware of what they're already taking.

Three of the six prescription drugs found in Ledger's apartment had been filled in Europe, where the actor was recently filming, police said.

"If you see one doctor for one thing and you see another doctor for another thing, neither the physician nor the patient may realize they're getting two similar medications," Prosser said.

"Patients should be aware that this happens on a regular basis and it doesn't just happen to celebrities."

Ledger's publicist, Mara Buxbaum, didn't immediately respond to questions about the drugs that had been prescribed to the actor before his death. She released a statement Wednesday from Ledger's father, Kim.

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

The medical examiner cited oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine as causing the actor's death. There was no mention of alcohol or illegal drugs.

Oxycodone, marketed as OxyContin, is used in other painkillers such as Percodan and Percocet; hydrocodone is used in a number of painkillers, including Vicodin.

Diazepam and alprazolam are the generic names for the anti-anxiety drugs Valium and Xanax, temazepam is a sleep aid sold as Restoril, and doxylamine is an antihistamine used in over-the-counter sleep aids and cold medicines.

Ledger's masseuse found him unresponsive after she arrived for an appointment at his rented apartment. She called 911 after first repeatedly calling actress Mary Kate Olsen. Ledger had moved into the apartment last fall after he broke up with actress Michelle Williams, the mother of his 2-year-old daughter Matilda.

Ledger, nominated for an Oscar for his role as cowboy Ennis del Mar in "Brokeback Mountain," had returned to New York from London, where he had been making a Terry Gilliam film, days before his death. He told The New York Times in November that his most recent completed roles in the Batman movie "The Dark Knight" and Bob Dylan biopic "I'm Not There" had taken a toll and caused him to lose sleep.

"Last week I probably slept an average of two hours a night," Ledger told the Times. "I couldn't stop thinking. My body was exhausted, and my mind was still going." He said he had taken two Ambien pills, which only gave him an hour of sleep.

Ledger's family returned to the actor's hometown of Perth, Australia, on Tuesday to prepare for his funeral. Arrangements were private.

"To most of the world, Heath was an actor of immeasurable talent and promise," Ledger's father said on Wednesday. "We knew Heath as a loving father, as our devoted son, and as a loyal and generous brother and friend."

Ledger's former girlfriend and "Brokeback Mountain" co-star Michelle Williams arrived in Perth for the actor's funeral with their 2-year-old daughter, Australian media reported. The ceremony, details of which are being kept secret by Ledger's family, is expected within days.

On Wednesday, Williams, dressed in black and carrying her daughter with Ledger, Matilda, arrived in Perth from New York, News Ltd. newspapers reported.

Ledger's parents and other close relatives arrived Tuesday in Perth after spending nearly two weeks in the U.S. immediately following his death. There was no indication that Ledger's remains have arrived in Australia, and there was no sign of activity at the family's plot in Karrakatta Cemetery on Wednesday.