According to CNN, that's more than three times the maximum adult daily intake recommended by the American Heart Association and nearly three times the amount of sugar in Coca-Cola, which contains nine teaspoons of sugar per can.

The report was published by British campaign group Action on Sugar, which describes itself as "a group of specialists concerned with sugar and its effects on health" and includes doctors, nutritionists and public health specialists. One of the group's aims is advising people how to eat less sugar.

The organization reported that Starbucks' most sugar-loaded drink is the hot grape mulled fruit chai tea, which contains 25 teaspoons of sugar in the largest size offering -- the same amount of sugar in five chocolate chip muffins. Twenty-five teaspoons of sugar is equal to 100 grams of sugar. The maximum adult daily intake of free sugars is seven teaspoons per day.

Action on Sugar says many Starbucks drinks are incorrectly perceived as healthy.

The report also reveals that a venti-sized white chocolate mochafrappucino with whipped cream contains 18 teaspoons of sugar and Starbucks' signature hot chocolate has 15 teaspoons of sugar in the venti size. The same size chai latte has 13, and the pumpkin spice latte with whipped cream has 10.

In comparison, a medium vanilla chai at Dunkin' Donuts has about 11 teaspoons of sugar and a hot macchiato at the same restaurant has seven. A large mocha at McDonald's has 11, and KFC's mocha contains 15.

"Earlier this year we committed to reduce added sugar in our indulgent drinks by 25 percent by the end of 2020," a Starbucks spokesperson said. "We also offer a wide variety of lighter options, sugar-free syrups and sugar-free natural sweetener and we display all nutritional information in-store and online."