Many energy drinks incorrectly list the amount of caffeine in their product, or do not list the amount at all, according to Consumer Reports.

The magazine tested 27 popular energy drinks and shots, and calculated the amount of caffeine in one serving, based on the manufacturer's serving size, according to CBS News.

Of those products, 16 listed specific caffeine amounts. Five products—Arizona Energy, Clif Shot Turbo Energy Gel, Nestle Jamba, Sambazon Organic Amazon Energy and Venom Energy—had 20 percent more caffeine per serving than stated on the label.

Archer Farms Energy Drink had 70 percent less caffeine than indicated on the label. The caffeine levels of the remaining products fell within 20 percent of the amount stated on the label.

Monster Beverage Corp. told CBS News its company does not list caffeine amounts 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."

The U.S. Food and Drug Administration (FDA) is investigating reports that five people have died since 2009 after they consumed Monster energy drinks. The investigation was announced after parents of 14-year-old Anais Fournier sued the company in connection with their daughter's death. The FDA said it has not established a connection between the drinks and the deaths.

Last year, the Substance Abuse and Mental Health Services Administration issued a report that found a sharp rise in the number of emergency department visits linked with the use of non-alcohol energy drinks, from 1,128 visits in 2005, to 13,114 in 2009. The report noted that energy drinks are marketed to appeal to youth, and are consumed by up to half of children, teenagers and young adults.

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