Imagine a country so fed up with its ineffective crime-and-punishment approach to drug abuse that it decriminalizes the possession of small amounts of narcotics for personal use.

At the same time, it launches a concerted effort to provide treatment for addicts instead of just throwing them in prison. Surely such a naive land would see a sharp increase in drug use, and perhaps a generation of youth blighted by easy access to mind-altering substances. But in Portugal, which is just such a country, that’s not what happened.

Drug use does seem to have gone up, but this increase might well be illusory — and rather harmless. What’s not illusory, on the other hand, is the sharp reduction in the ills associated with drug abuse. Nine years into its courageous experiment with sanity as a national drug policy, Portugal is indisputably better off. And it’s getting some well-earned attention for its efforts.

Policymakers in this country ought to pay especially close attention, given the colossal futility of our own endless “war on drugs” — for never has a cure been so much more catastrophic than the disease it was intended to remedy.

With 2.3 million inmates, America now has the largest prison population in the world — and the highest per-capita rate of incarceration as well.

Our absurd drug laws play a big part in this: A quarter of U.S. inmates are nonviolent drug offenders. Incarceration is expensive — in New York, it costs about $45,000 per inmate annually, not counting pensions and other benefits for prison staff. We can no longer afford to lock up so many of our fellow citizens, and so now there is pressure all over America to cut the number of inmates.

This makes the Portuguese experience particularly noteworthy at the moment. A study in the British Journal of Criminology by Caitlin E. Hughes and Alex Stevens lays it all out. The bad news is that, as you might expect, the price of drugs in Portugal has fallen since the reforms, and there has been some increase in drug use among adults. But neighboring Spain, which didn’t change its laws, also saw an increase in drug use. And the finding in Portugal might simply reflect users’ greater willingness to admit their indulgence to pollsters since the law’s relaxation.

Even if the increase is real, it doesn’t much matter, because the harms associated with drug abuse are so much diminished. Before decriminalization, for example, Portugal had the highest rate of drug-related AIDS in the European Union. But in the years since, the infection rate has plunged thanks to syringe programs, methadone and outreach efforts. Overdose deaths are down, and more addicts are in treatment.

As to prisons: Since the new law, arrests for crimes related to drugs have fallen by almost two-thirds. Prisons fell from 119 percent of capacity to 102 percent. And the proportion of inmates incarcerated for drug-related crimes was halved.

A key factor in Portugal’s success: treatment and dissuasion (via counseling, community service and other measures) have been integral parts of its drug reforms from the outset.

Portugal’s, in other words, was a comprehensive reform. The Portuguese experience should embolden us to try something sensible here. America’s war on drugs is a costly failure on a larger scale than was Prohibition, with ramifications far beyond our borders.

We’ll never eliminate drugs for the simple reason that too many people like them. But it’s time to figure out a way to decriminalize narcotics, at the very least, even while firmly discouraging their use.

Daniel Akst, a columnist for Newsday, is the author of “We Have Met the Enemy: Self-Control in an Age of Excess.”