If you've been drinking green tea for its health benefits, you may be in for a jittery surprise: ounce for ounce, it has more caffeine than a can of Classic Coke.
Red Bull, which once was the ultimate go-to energy drink, has just 9.5 mg per ounce -- about as much as a Starbucks latte.
Coffee's caffeine content can depend on how the coffee is prepared: Drip coffee has 18.1 mg per ounce, brewed coffee has 13.4 mg per ounce, and instant coffee has just 7.1 mg per ounce. Your mileage may vary among the coffee-shop giants, too: Dunkin' Donuts' coffee has 13.2 mg of caffeine per ounce, compared to 15 mg for Caribou Coffee, 9.1 mg for McDonald's, and 20.6 mg for the regular brew at Starbucks.
Sodas: While A&W root beer is caffeine-free, Barq's has 1.9 mg per ounce. Classic Coca-Cola had 2.8 mg per ounce, Pepsi had 3.2 per ounce, Diet Coke has 3.8 mg per ounce, and the myth of Mountain Dew is debunked, given that it has less caffeine than Diet Pepsi Max.
Moderate amounts of caffeine (200 to 300 mg per day) aren't harmful. But knocking back 500 to 600 mg worth every day (that's about four cups of regular coffee, or two to three energy shots) can lead to a host of physical problems.