Many years ago, when I was in graduate school, a professor asked me why Americans feared some drugs more than others. Timidly, I mumbled something about the dangers of addiction.

My professor smiled, in the knowing but slightly patronizing way that teachers correct their students. “It’s not about the drug,” he said. “It’s about who uses it.”

I’ve been thinking about his comment as our presidential candidates sojourn through New Hampshire, which is in the midst of the worst heroin epidemic in its history. Whereas earlier generations of politicians demanded stiffer penalties for heroin use, our current crop is emphasizing treatment and prevention. And there’s one big reason for that: Most of the heroin addicts in New Hampshire are white.

That mirrors the larger pattern around the country, where 90 percent of people who tried heroin for the first time over the past decade were white. Use has risen especially sharply in rural and suburban areas, which have also witnessed a steep spike in addiction to opiate-derived painkillers. So politicians are more forgiving towards heroin and other opiates than they were in the past, when the drug was more strongly concentrated in urban and minority communities.

Ironically, the first wave of opiate addiction in the United States was also a predominantly white affair. In the late 1800s, doctors prescribed morphine to Civil War veterans to relieve what we’d call post-traumatic stress disorder. Opium-based products also became popular among well-to-do women afflicted with “neurasthenia,” or weak nerves. ...