The chocolate charge was part of a raft of fiscal changes passed by Mexico's Congress on Thursday that seek to boost tax revenues and to tackle the country's unhealthy eating habits.
Among the amendments added to the tax bill was a levy on "junk food" - defined as products containing more than 275 calories per 100 grams. Many types of chocolate have around twice that amount.
McDonalds hamburgers, for example, fall below the benchmark, according to data on the company's website.
Originally proposed as a 5 percent levy this month, Congress approved an 8 percent charge on the foods.
Chocolate was grouped alongside a host of high-calorie products including gelatine, sweets and some puddings.
Etymologists trace the origin of the word "chocolate" to the Aztec word "xocolatl." It refers to the foamy bitter drink brewed from cacao - or cocoa - beans, according to the website of Washington's Smithsonian Institution.
In Aztec times, the drink was reserved for the nobility.
Historians say cocoa beans were also used like currency in many parts of pre-modern Latin America, and the Maya and Aztecs believed the bean had magical properties.
Legend has it that Aztec king Moctezuma feted Spanish conquistador Hernan Cortes with drinking chocolate when he arrived to conquer Mexico in the early 16th Century.
