The nation’s first soda tax is apparently having the desired effect.

A new study shows the penny-per-ounce tax on soda and other sugary drinks implemented in Berkeley, California, in March of 2015 has curbed consumption by at least one-fifth in the city’s low-income neighborhoods.

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Berkeley voters approved the tax in an effort to curb consumption and stem the rising tide of diabetes and obesity. The new numbers, published in the October American Journal of Public Health, show that residents of two low-income neighborhoods are consuming 21 percent fewer sugar-sweetened beverages and 26 percent less soda than they had the year before.

“From a public health perspective, that is a huge impact,” senior author Dr. Kristine Madsen said in a telephone interview with Reuters. “That is an intervention that’s more powerful than anything I’ve ever seen aimed at changing someone’s dietary behavior.”

The soda industry has spent millions to defeat taxes on sugary drinks in dozens of U.S. cities — while others believe this is government overreach. But the tax passed easily in Berkeley with 76 percent of the vote. The measure covers sweetened fruit-flavored drinks, soda, energy drinks like Red Bull, and caffeinated drinks like Frappuccino iced coffee. Diet beverages are exempt.

Related: That Soda Addiction Will Cost You

The only other city to implement a sugar tax is Philadelphia. That city’s 1.5-cent-per-ounce tax is set to take effect in January 2017, although soda trade groups have sued to try to block the measure. Voters in Boulder, Colorado, and the Bay Area cities of San Francisco, Oakland and Albany will vote on whether to tax sugary beverages on Nov. 8.