Media coverage of the primary in New Hampshire has underlined an unwelcome and alarming fact: There is an epidemic in the use of heroin in New Hampshire. How come?

Haven’t we had a war on drugs for the past 40 years?

Why hasn’t it been as effective as the war on smoking?

The Surgeon General estimates that reducing the rate of smoking in the U.S.—to 18% of the population today, down from 43% immediately after that office’s landmark 1964 report warning about the danger of smoking—has saved millions of lives and avoided hundreds of billions of dollars in health-care spending by preventing smoking-associated chronic diseases. As a public-health campaign, it was relatively cheap, and the efficacy was enormous. It is preventive medicine’s greatest success story.

Let’s do the same thing on the program of drugs. They are bad for people and society, so let’s campaign against their use and dramatize to people—especially young people—the damage they’re doing to their brains and their bodies through the use of drugs.

We should also invest more money and effort in treatment centers so that people have a place to go where professional help will be available. At the present time, no one would go because taking drugs is illegal and he or she would be arrested. A young black child caught with marijuana will be sent to jail, where he will learn how to become a real criminal.

Let’s decriminalize the use of drugs so that treatment centers can work. Keep the peddling of drugs criminal so you can go after the dealers, but let’s persuade young people not to damage themselves the way they’re doing with drugs.

If this takes place, we can also take the profit out of the drug trade and thereby pull the rug out from under drug gangs that are using money and weapons from the U.S. criminalized drug market to disrupt societies to our south, especially Mexico and Central America.

So let’s have an urgent effort to encourage people—especially young people—to stop taking drugs. As Nancy Reagan once campaigned, “Just say No.” That’s the way to win the war.

Mr. Shultz, a former secretary of labor, Treasury and state, and director of the Office of Management and Budget, is a distinguished fellow at Stanford University’s Hoover Institution.

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