Casting about for a reason why Rudy Eugene gnawed off most of a homeless man's face in an unprovoked attack on Miami's MacArthur Causeway last month, his girlfriend suggested he may have been the victim of a voodoo curse. Or maybe he was drugged, she told The Miami Herald, adding, "I don't know how else to explain this."

While the voodoo hypothesis did not gain much traction, the idea that drugs turned Eugene into the "Miami Zombie" was repeated by one news outlet after another, even though there was little more evidence in its favor. This pattern of credulous reporting, characteristic of drug panics, reflects our perennial readiness to believe that satanic substances hijack people's souls and compel them to sin.

As "Theodoric of York, Medieval Barber" in an old Saturday Night Live sketch, Steve Martin tells a patient's father that people once foolishly believed disease was caused by demonic possession, but "nowadays we know that Isabelle is suffering from an imbalance of bodily humors, perhaps caused by a toad or a small dwarf living in her stomach." Likewise, whereas people used to think the devil was the source of evil, today we know that drugs are—even if we're not sure which drugs, or whether a particular criminal has actually consumed them.

A few days after Eugene's grisly assault, which a police officer stopped by shooting him dead, the head of the local police union, Armando Aguilar, declared that Eugene must have been on "bath salts," quasi-legal stimulants that are sold over the counter, ostensibly "not for human consumption." Aguilar's speculation, which was uninformed by toxicological tests, spawned alarmist headlines like "Bath Salts, Drug Alleged 'Face-Chewer' Rudy Eugene May Have Been On, Plague Police and Doctors" (CBS News) and "Miami's 'Naked Zombie' Proves Need to Ban Bath Salts, Experts Say" (U.S. News & World Report).

The media frenzy started with WFOR, the CBS affiliate in Miami. "We have seen, already, three or four cases that are exactly like this," Aguilar told the TV station. Later, in an interview with ABC, he clarified that "the cases are similar minus a man eating another"—i.e., the single most salient aspect of Eugene's crime. Quoting Aguilar and a local emergency room physician, WFOR said people who use what it called "the new LSD" (even though "bath salts" and LSD are very different in their chemistry and effects) have "super-human strength," such that six men might be required to restrain a single individual.

Stories about psychoactive substances that transform people into irrationally violent monsters with superhuman strength have been tied to various chemical agents over the years, including cocaine, PCP, methamphetamine, and even marijuana. They always prove to be grossly exaggerated, if not utterly fictitious.

A 1989 analysis of "crack-related homicides" in New York City, for example, found that the vast majority of the violence stemmed from black-market disputes, as opposed to the drug's psychoactive effects. After finding only three documented cases in which people under the influence of PCP alone had committed acts of violence, the authors of a 1988 literature review concluded that "PCP does not live up to its reputation as a violence-inducing drug."

That does not mean people who use these drugs are never violent. But focusing on extreme cases and presenting them as typical—as police, E.R. physicians, psychiatrists, reporters, and politicians tend to do—suggests such incidents are much more common than they actually are.

It is clear that drugs do not "cause" violence in any straightforward way. Otherwise, given the millions of people who have used drugs reputed to trigger violence, we'd have a lot more murder and mayhem.

By mindlessly repeating the claim that "bath salts" made Eugene eat a man's face, the press asks us to believe these drugs are disturbingly popular even though they commonly cause outbursts of vicious violence in otherwise pacific people. If that seems plausible to you, you may be qualified to write about drugs for a major news organization.

Jacob Sullum is a senior editor at Reason and a nationally syndicated columnist. Follow him on Twitter.