The buzz on energy-drink caffeine

They're everywhere: beverages that promise to keep you energized, revved, and alert. But labels don't have to reveal how much caffeine the products pack. We will. We measured the amount in 27 top-selling energy drinks and shots (see table below).

We bought the drinks online or at stores in Connecticut, New Jersey, and New York, and tested three lots of each product, choosing one flavor, usually fruit. We also sent shoppers to stores all across the U.S. to see where energy drinks are displayed. (Our shoppers usually found energy drinks near soda and juice, sometimes at checkout, and less often near alcoholic beverages. That's good, since the potential for intoxication in people who mix energy drinks and alcohol is a concern.)

What we found. Caffeine levels per serving ranged from about 6 milligrams to 242 milligrams per serving—and some containers have more than one serving. The highest level was in 5-hour Energy Extra Strength; the lowest in the seemingly oxymoronic 5-hour Energy Decaf. (The company says it's for people who want to limit caffeine but still get a blend of nutrients that provides "an energy boost and a sustained feeling of alertness.") By comparison, an 8-ounce cup of coffee has about 100 milligrams; a 16-ounce Starbucks Grande, 330 milligrams.

Five of the 16 products that list a specific amount of caffeine—Arizona Energy, Clif Shot Turbo Energy Gel, Nestlé Jamba, Sambazon Organic Amazon Energy, and Venom Energy—had more than 20 percent above their labeled amount on average in the samples we tested. On the other hand, one of our three samples of Archer Farms Energy Drink Juice Infused had caffeine about 70 percent below the labeled amount. For the other drinks that list caffeine levels, the actual numbers were within 20 percent of claimed, which we think is an acceptable range for meeting caffeine claims.

Eleven of the 27 drinks don't specify the amount of caffeine. Why the secrecy? Their blends may be proprietary. (Common blends include amino acids, carbohydrates, or guarana, a botanical caffeine source.) A representative of the Monster Beverage Corporation provided another reason: The company doesn't list levels "because there is no legal or commercial business requirement to do so, and also because our products are completely safe, and the actual numbers are not meaningful to most consumers." Yet labels on both tested Monster drinks—like those of 16 other products—warn against use by children, pregnant or nursing women, and people sensitive to caffeine. The Monster drinks and eight others also recommend a daily limit.

Consumer and scientific groups have for years urged the Food and Drug Administration to make companies disclose caffeine levels, but the agency says it lacks the authority.

Bottom line. Caffeine can make you feel more alert, boost your mental and physical performance, and even elevate your mood. But it can also make you jittery, keep you from sleeping, cause rapid pulse or abnormal heart rhythms, and raise blood pressure.

For more information about a cup of coffee vs. 5-Hour Energy check our article and watch the video about how well 5-Hour Energy really works.

Safe limits of caffeine consumption are still being studied, but data suggest that most healthy adults can safely consume up to 400 milligrams per day; pregnant women, up to 200 milligrams; and children, up to 45 to 85 milligrams depending on weight. An occasional energy drink is probably fine for most adults. Check the Ratings for caffeine levels and price. And note that some products cost less than half as much as others per serving.