Tom Petty died from, according to the New York Times headline, an "Accidental Drug Overdose." Here's the coroner's list of the drugs found in Petty's system:
fentanyl, oxycodone, temazepam, alprazolam, citalopram, acetyl fentanyl and despropionyl fentanyl.

Petty's death is not accurately classified as an overdose. He died due to a dangerous mixture of opioid drugs. Such drug intake, often classified as "chaotic" drug use, is the source of over 90% of deaths involving drugs, so much so that the CDC now classifies these deaths as "drug poisonings" rather than as "overdoses."

"But what concerns me even more are the last two drugs: acetyl fentanyl and despropionyl fentanyl. These are nonprescription, synthetic opioid relatives of fentanyl that are not used medically. Despropionyl fentanyl is better known by its acronym, ANPP is more often seen as an illicit chemical precursor in the synthesis of other designer fentanyls and, according to Cayman Chemical, is sometimes found as an unreacted impurity in illicit fentanyl preparations. How Petty might have been exposed to these two compounds on top of the prescription opioids is concerning.