Starbucks Doubleshot Energy is a 15 oz, ready-to-drink coffee beverage containing 210 calories, 10-12g of protein, and a significant boost from 145mg to 225mg of caffeine per can depending on the specific flavor, often blended with guarana, B vitamins, and ginseng. Available flavors include Mocha, Vanilla, Caramel, and White Chocolate, generally providing a sweet, creamy, and bold coffee taste.