WikipediaWikipediaOn Friday the New York City medical examiner's office released autopsy results indicating that the actor Philip Seymour Hoffman died accidentally on February 2 from "acute mixed drug intoxication" involving cocaine, amphetamine, and benzodiazepines as well as heroin. The combination of heroin and benzodiazepines, a class of drugs that includes Valium and Xanax, presumably was what killed him, since both depress respiration. The stimulants may have masked the effects of the depressants, leading Hoffman to consume more than he otherwise would have.

Drug combinations like this are typical of deaths attributed to heroin or other narcotics. Data from the Drug Abuse Warning Network (DAWN) indicate that "multi-drug deaths" accounted for most fatalities involving opiates or opioids in 2010: 72 percent in surburban New York, 83 percent in Los Angeles, and 56 percent in Chicago, for example. Back in the early 1990s, the share of heroin-related deaths reported by DAWN that involved other drugs was even higher, 90 percent or more. (Note that the numbers in the table are misaligned and need to be shifted downward.) In short, when someone dies from what is described as a heroin overdose, the actual cause is usually a fatal mixture of two or more substances, frequently including depressants such as alcohol or prescription tranquilizers.

That fact can make it difficult to assign legal blame for an "overdose" death. Under federal law, for instance, a drug dealer faces a 20-year mandatory minimum sentence when "death or serious bodily injury results from" consumption of his product. In January the Supreme Court unanimously ruled that when a death involves multiple drugs, the prosecution has to show that the one supplied by the defendant was a necessary or independently sufficient factor.

Under New York law such a case is even harder to make. According to a 1972 decision that was upheld by the state's highest court, a drug dealer is not guilty of criminally negligent homicide merely for supplying heroin and syringes to someone who died after injecting the narcotic. Prosecutions for criminally negligent homicide have been upheld in cases where the defendant played a more active role in someone's death—for example, by injecting him with heroin or encouraging excessive alcohol consumption in the context of a drinking game. The musician suspected of supplying heroin to Hoffman, Robert Vineberg, has been charged with felony drug possession, but so far he has not been accused of homicide.

Given the circumstances of the typical heroin-related death, avoiding risky drug combinations is an obvious harm reduction measure that should be promoted by anyone interested in preventing such fatalities. Yet it is rarely mentioned in the aftermath of high-profile overdoses such as Hoffman's, perhaps because of a bias against advice that aims to make drug use less dangerous rather than eliminate it completely. As I have argued, that all-or-nothing attitude may also help explain why Hoffman was so reckless once he fell off the wagon.