Soda in Philadelphia is now 40 percent more expensive—here’s how consumption has changed.

After first making headlines in New York City in 2010 (and generating heated responses from health professionals and the beverage industry), the concept of a "soda tax" has grown into a reality for almost nine million Americans. But one new piece of evidence might settle the debate of whether taxing soda could improve the health of consumers once and for all.

In 2017, Philadelphia became one of the eight cities in the nation to implement a soda tax. Each soda in the city was taxed 15 cents per ounce—an estimated 20 percent upcharge from the usual price. A team of researchers within Philly's Drexel University closely followed the effects of the tax over the last year and published a study in the American Journal of Preventive Medicine after finding strong evidence that the tax had a direct effect on how much soda residents were drinking.

The study shows the soda tax led to a 40 percent reduction in daily consumption among local residents in the first two months after it went into effect. The researchers also found an immediate 38 percent drop in the total number of sodas sold and consumed in a 30-day period.

Using data collected from 1,000 men and women in Philadelphia, researchers compared their responses to those living in nearby cities like Trenton, New Jersey and Wilmington, Delaware. The responses showed that Philadelphia residents were 40 percent less likely to drink soda after the tax was passed, and nearly 65 percent less likely to drink energy drinks, Time reports.

Researchers said that diet beverage sales didn't suffer as much as other categories, and other sugar-heavy fruit drinks that weren't taxed—such as lemonade or cranberry juice—didn't suffer a sales slump at all.

Credit: Lidia Camacho / Getty

Some believe the evidence collected so far isn't enough to say these taxes are "working”, and the study is unclear on whether the steep decline in sales continued after the first two months in 2017, but the evidence mounting in support of taxing sugary soft drinks is getting hard to ignore.

A recent analysis by the World Health Organization showed that a 20 percent tax on junk food or unhealthy drinks leads to a long-lasting 20 percent decrease in consumption. With Philly's tax at upwards of 40 percent, we're thinking (and hoping) that it might be a while before sales return to normal levels.