MEXICO CITY >> America’s drug problem is shifting from illicit substances like cocaine to abuse of prescription painkillers, a change that is forcing policymakers to re-examine the long and expensive strategy of trying to stop illegal drugs from entering the United States.

This rethinking extends beyond the United States, where policymakers are debating how to better reduce demand for painkillers. The effects would also be felt here and in Central America: With the drug wars in Mexico flaming violence, some argue that the money now used for interdiction could be better spent building up the institutions — especially courts and prosecutors’ offices — that would lead to long term stability in Mexico and elsewhere.

‘’The policies the United States has had for the last 41 years have become irrelevant,” said Morris Panner, a former counternarcotics prosecutor in New York and at the U.S. Embassy in Colombia, who is now an adviser at Harvard’s Kennedy School of Government. “The United States was worried about shipments of cocaine and heroin for years but whether those policies worked or not doesn’t matter because they are now worried about Americans using prescription drugs.”

While a major change in policy is not imminent — “It’s all aircraft carriers, none of it moves on a dime,” as one senior Obama administration official put it — the election of a new president in Mexico, Enrique Pena Nieto, is very likely to have an immediate impact on the debate. Pena Nieto has promised to focus not on drugs but rather on reducing the violent crimes that most affect Mexicans.

Mexico and its neighbors, especially Honduras, El Salvador and Guatemala, are withering under a metastasizing threat: violence caused by drug traffickers battling for power, to move drugs, extort businesses and kidnap and kill for ransom. The U.S. response so far has mostly involved a familiar escalation of force, characterized by the addition of law enforcement and military equipment and personnel to help governments too weak to combat trafficking on their own.

But in Mexico, a focus of U.S. anti-drug efforts in recent years, a shift in priorities is already apparent. Since 2010, programs for building the rule of law and stronger communities have become the largest items in the State Department’s anti-drug budget, with the bulk of the money assigned to Mexico. That amounts to a reversal from 2008 and 2009 when 70 percent was allocated to border security and heavy equipment like helicopters.

Even some officials with the Drug Enforcement Administration and Justice Department say they now recognize that arresting kingpins and seizing large drug shipments have failed to make Mexico more stable, largely because of corruption and other flaws in the Mexican justice system.

U.S. officials say they are now focused on training Mexican prison guards, prosecutors and judges, while supporting Mexican programs aimed at keeping at-risk youths from joining gangs.

‘’We see crime as the leading threat in some countries to economic growth and the leading threat to democracy,” said Mark Feierstein, the U.S. Agency for International Development’s assistant administrator for Latin American and the Caribbean.

Still, law enforcement remains a major element of the government’s strategy, as the deployment of a commando-style squad of Drug Enforcement Administration agents in Honduras has demonstrated. And the Obama administration has ruled out drug legalization, despite expanding support for the idea in Latin America, while designating about 60 percent of the federal anti-drug budget of roughly $25 billion a year to supply side efforts, with 40 percent to demand, as it has for decades.

Eric L. Olson, a security analyst with the Woodrow Wilson International Center for Scholars, said the growing debate has, so far, mostly led to confusion. “Some U.S. officials favor building institutions; others think it’s hopeless,” he said.

Other experts are more critical of the Obama administration, pointing to the continued focus on cocaine interdiction, especially in Honduras where commando-style DEA teams have been involved in a series of recent raids, including one that left four people dead, including two pregnant women, and another one, last week, in which two people who were said to be smugglers were killed.

‘’It just hasn’t worked,” said Mark L. Schneider, a special adviser on Latin America at the International Crisis Group. “All interdiction and law enforcement did was shift cultivation from Colombia to Peru, and the increase in interdiction in the Caribbean drove trafficking to Mexico, and now with the increase in violence there it has driven trafficking to Central America as the first stop. So it is all virtually unchanged.”

What has changed is Americans’ use of cocaine.

The most recent National Survey on Drug Use and Health found 1.5 million people who had used cocaine in the past month, down from 2 million in 2002 and, according to an earlier government survey, 5.8 million in the mid-1980s. (Methamphetamine use has also fallen in recent years, while heroin use is up somewhat, to 239,000 monthly users in 2010 from 213,000 in 2008.)

Some officials argue the cocaine decline shows that supply side efforts have worked, but experts note that prices in the United States have held mostly steady since the late ‘80s, suggesting that decreasing demand is the main cause. Mark A.R. Kleiman, a professor of public policy at the University of California, Los Angeles, said that in the United States, cocaine has simply run its course among aging addicts. “What you’re recording,” he said, “is the rate at which they are dying or quitting.”

Now the drugs most likely to land Americans in emergency rooms cannot be interdicted.

Studies show that prescription painkillers, and stimulants to a lesser extent, are the nation’s biggest drug problem. The same survey that identified 1.5 million cocaine users in 2010 found 7 million users of “psychotherapeutics.” Of the 36,450 overdose deaths in the United States in 2008, 20,044 were from prescription painkillers, more than all illicit drugs combined.

And whereas cocaine and heroin have been concentrated in big cities, prescription drug abuse has spread nearly everywhere. “Today there is drug use in every county in Ohio, and the problem is worse in rural areas,” said Mike DeWine, the attorney general of Ohio.

‘’This is an urgent, urgent issue that needs to be addressed promptly,” said Dr. Nora D. Volkow, director of the National Institute on Drug Abuse. So far, she said, the response from government and the health care industry has been inadequate.

But momentum for a broader change in domestic drug policy — as in foreign policy — appears to be building. DEA officials say they have recently created 37 “tactical diversion squads” focusing on prescription drug investigations, with 26 more to be added over the next few years.

‘’Unfortunately,” said Rep. Mary Bono Mack, R-Calif., chairwoman of the Congressional Caucus on Prescription Drug Abuse, “it’s because more and more members are hearing from back home in their district that people are dying.”