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.