LAST year, voters in Colorado and Washington state approved initiatives legalizing the recreational use of marijuana. While the details are being worked out, those watching the developments are not only in the United States.Mexico, too, is taking note, having paid an enormous price waging a costly — and, to a certain degree, futile — yearslong crusade against drugs in consonance with the international community’s punitive approach.A growing number of Mexicans are asking logical questions: Why should their leaders follow a path that provokes violence, generates human-rights violations, erodes the country’s image abroad and costs a fortune — mainly to stem the northern flow of drugs?Why spray and uproot marijuana fields in the hills of Oaxaca, search for tunnels in Tijuana and incarcerate weed traffickers in Monterrey if consumption is made legal in parts of the United States?Why deploy such an enormous effort to deter drug trafficking if Washington does virtually nothing to stop the flow of firearms to Mexico — and has concluded that it can, and should, prevent migrants from Mexico and Central America from entering the United States?If Congress can “secure” the border against people, using walls and drones, why can’t it do the same against drugs or guns and, in the process, respect Mexico’s right to design its own policies?These sentiments are part of the reason for a change in Mexican attitudes toward drugs in general and marijuana in particular. Two former presidents — Ernesto Zedillo and Vicente Fox, who both vigorously fought drug trafficking and consumption while in office — have concluded that this approach is doomed and that a better policy would include decriminalizing marijuana use and commerce.Then-President Felipe Calderón called on the U.N. General Assembly last year to change its focus, eliminating the perverse incentives that strengthen transnational organized crime and gravely affect the rule of law and democracy in some countries.Mexico is a highly conservative country whose population remains largely opposed to legalizing marijuana. But an increasing number of business, political and academic leaders are shifting their views.The city council of Mexico City, which has authority to legislate health and law-enforcement issues, is contemplating a measure that would, in effect, allow the regulated possession and use of marijuana.Already, Mexicans can legally possess five grams of marijuana, an amount much smaller than what is commonly sold, bought or shared. Effectively decriminalizing marijuana would be in line with liberal attitudes in the capital and laws that rest on the firm belief that the right to privacy includes certain personal choices, even — or especially — when not shared by the majority.We and other former cabinet secretaries — Pedro Aspe, finance minister to Carlos Salinas, and Juan Ramon de La Fuente, health minister to Zedillo — have joined with Mexico’s leading public intellectual and a prominent social activist to push for legalization in Mexico City.The four of us occupied senior posts directly related to the drug issue in Mexico’s previous four administrations. Along with Hector Aguilar Camin, editor of the monthly Nexos, and Maria Elena Morera, founder of Mexico Unido Contra la Delincuencia (Mexicans United Against Crime), we are encouraging Mexico City authorities to proceed promptly.For practical and political reasons, our effort is limited to decriminalizing the use of marijuana in the federal district, though some believe that the same case can be easily made for other drugs in the whole country.A reform that restrains its effects to marijuana is achievable; going further does not seem feasible today. Another reason for moving slowly, though firmly, is the impact this decision would have on the relationship between Mexico and the United States.President Enrique Peña Nieto opposes legalization but seems open to a broad debate and to whatever consensus would emerge — locally, nationally or regionally. He may accept Mexico City’s decision even if he doesn’t like it, much as President Obama seems to have resigned himself to the Colorado and Washington legislation.Mexico has ratified treaties banning illicit substances, but these international agreements allow governments to set their own policies within certain limits; consider Dutch and Portuguese leniency. The United States should support its neighbor as it seeks leeway for its own stance, even if that conflicts with U.S. policy.Mexicans have paid a high cost in the struggle against drugs. We know that this war cannot be won. This fight should be waged by physicians rather than armed forces.Decriminalization of marijuana is not a silver bullet, but it would be a major step away from a failed approach. Mexico City is the place to start, thanks to the example set in Colorado and Washington state.Fernando Gomez Mont was Mexico’s interior minister in the administration of Felipe Calderón. Jorge Castañeda was minister of foreign affairs in the administration of Vicente Fox.