For about a decade now, policy makers and the soda industry have been fighting about the idea of a big soda tax. Proponents say it would fight obesity by reducing consumption of sugary drinks. A leading objection by the industry is that the tax simply would not work.

Those discussions were largely theoretical, because no big city, state or country had passed the kind of tax that advocates wanted.

That recently changed. In 2013, Mexico passed a tax right out of the public health literature. And now the theoretical debate is becoming more real. Preliminary data from the Mexican government and public health researchers in the United States finds that the tax prompted a substantial increase in prices and a resulting drop in the sales of drinks sweetened with sugar, particularly among the country’s poorest consumers. The long-term effects of the policy remain uncertain, but the tax is being heralded by advocates, who say it could translate to the United States.

“It’s exactly what we thought the tax would do,” said Barry Popkin, a professor of nutrition at the University of North Carolina, whose team conducted the research.

The idea for the soda tax is in some ways modeled on the tobacco taxes passed by states and the federal government over the last few decades. The idea of those taxes was not only to raise revenue — though that was a nice side effect — but also to discourage people from buying cigarettes. A robust literature now exists showing that the resulting higher prices really did push down cigarette sales, particularly among young people.

Similarly, the idea for the soda taxes is that they should be applied to bottlers or retailers, so that the prices show up on price tags, not at the cash register. As with the most effective cigarette taxes, proponents want them to be large enough that customers notice the difference.