Looks like Heath died from accidental overdose

http://www.wnbc.com/news/15224103/detail.html

NEW YORK -- The medical examiner has concluded that actor Heath Ledger's death was an accident, and the result of the abuse of prescription medications.

The medical examiner released results of the toxicology report Wednesday, saying Ledger died as the result of acute intoxication by the combined effects of six drugs, including pain killers, sleeping pills, and anti-anxiety drugs.
The six drugs found in his system were oxycodone, hydrocodone, diazepam, temazepam, alprazolam, and doxylamine, the medical examiner's office said.

The drugs are the generic names for the OxyContin painkiller, the anti-anxiety drug Valium, Xanax, an anti-anxiety drug, and the sleep aids Restoril and Unisom. Hydrocodone is another name for the better-known Vicodin.

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That's about what I figured.
The OxyContin and Vicodin, although prescription drugs, show he definitely had a drug problem.
They didn't list any condition he needed pain-killers for.