Heath Ledger died of an accidental overdose of painkillers, sleeping pills, anti-anxiety medication and other prescription drugs, according to medical examiners.
"What you're looking at here is the cumulative effects of these medications together," said spokeswoman Ellen Borakove.
The verdict arrives a fortnight after the 28-year-old Aussie star was found dead in his New York apartment. Police say no foul play occurred.
Ledger had admitted in an interview with The New York Times in November that he was having troubling sleeping and that his roles in Chris Nolan’s The Dark Night and Bob Dylan biopic had taken a toll on him.
"Last week I probably slept an average of two hours a night," said Ledger. "I couldn't stop thinking. My body was exhausted and my mind was still going."
A statement from Ledger's father, Kim, read: "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.”