-- How much caffeine is in your energy drink?

Don't count on finding out by reading the product label, a Consumer Reports (CR) investigation finds.

The consumer group tested 27 popular energy drinks. Eleven didn't list the amount of caffeine on the label. Among the 16 products that did, five had more than 20% more caffeine than the label claimed. One had about 70% less.

But all of the products had one thing in common: caffeine. Many had lots of caffeine. That raises a red flag for Gayle Williams, CR's deputy health editor.

"The amount of caffeine in these products is worrisome," Williams says. "They tout that they are as safe as coffee, but maybe not. They have a lot more caffeine than an 8-ounce cup of coffee."

That 8-ounce cup of coffee has about 100 milligrams of caffeine, although coffees and teas vary widely in their caffeine content depending on how they are brewed. For example, CR finds that 8 ounces of Starbucks coffee has 165 milligrams of caffeine.

CR says safe limits of caffeine are up to 400 milligrams per day for healthy adults, 200 milligrams a day for pregnant women, and up to 45-85 milligrams per day for children, depending on weight.

Not all of the makers of energy drinks are members of the American Beverage Association, the trade group that represents the soft drink industry. The ABA says its members' energy drink labels do list caffeine amounts.

"As an association, we are setting a leadership example in the energy drink category through our adoption of voluntary policies, including listing total caffeine amounts from all sources on beverage labels," the ABA's response to the CR survey says. "This voluntary policy, along with others covering marketing to children and school sales, is outlined in the ABA Guidance for the Responsible Labeling and Marketing of Energy Drinks, which is available on our web site and has been adopted by The Coca-Cola Company, Dr Pepper Snapple Group, PepsiCo, and Red Bull North America."

How Much Caffeine?

The consumer group bought three samples of each of the 27 energy drinks and tested them for caffeine. The highest amount per serving was 242 milligrams of caffeine in 5-Hour Energy Extra Strength. The lowest was in 5-Hour Energy Decaf, which despite the name carries 6 milligrams of caffeine per serving.

Caffeine can result in restlessness, nervousness, insomnia, and tremors. High amounts can also trigger seizures and abnormal heart rhythm.

Here are the results of the CR tests: 

Monster Energy, the drink blamed in a lawsuit for the death of a 14-year-old girl and cited in five deaths reported to the FDA, has 92 milligrams of caffeine per 8-ounce serving. That's about mid-range for the energy drinks tested -- but more than the lawsuit alleges the product contains.

"Neither the science nor the facts support the allegations that have been made," Monster Beverage Corp. says in a statement. "Monster reiterates that its products are and have always been safe."

Another thing that worries Williams is that energy drinks are marketed to teens and young adults.

"These drinks are accessible to kids; they are sold in stores near the soft drinks," she says. "And a lot of kids look at these drinks as a healthier alternative to soda. They may think it is better for them than sugary soft drinks."

The study findings appear in the December issue of Consumer Reports.

SOURCES:Gayle Williams, deputy health editor, Consumer Reports.Consumer Reports, December 2012.Medscape: "Caffeine Toxicity."Monster Beverage Corporation.

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