According to a study conducted by this Journal of Analytical Toxicology report, “the caffeine content of decaffeinated coffee obtained from different establishments was variable ranging from none detected to 13.9 mg per 16-oz serving …the finding that decaffeinated coffee contains caffeine has far-reaching clinical consequences. Clinicians and patients should be aware that decaffeinated coffee frequently contains caffeine. Ingestion of multiple servings of decaffeinated beverages could result in caffeine doses equivalent to a caffeinated beverage,”
— the average caffeinated coffee contains between 90-200 mg of caffeine, that means if you drink 5-10 cups of decaffeinated coffee, the dose of caffeine could be equal to the level present in a cup or two of caffeinated coffees. According to The Center for Science in the Public Interest, 12 oz. of Coca-Cola, Coke Zero, or Diet Pepsi contains 35 mg. of caffeine – about the same amount of caffeine as 3 cups of decaffeinated coffee.
This can mean bad news for people on prescription medications that interact negatively with caffeine, or have have medical conditions that require them to stay away from caffeine, like kidney disease or anxiety disorders.
Even more disturbing, Health.com reported that “in 2007 Consumer Reports tested 36 cups of decaffeinated coffee from six coffee standbys, including Starbucks and Dunkin’ Donuts. Compared to the caffeine found in a regular cup (generally around 100 milligrams), the decaf samples had less, but some packed in over 20.”