Caffeine drinks pose hidden danger, report says

>>> there is something a lot of people buy in the news tonight, consumer reports is out with a new investigation on how much caffeine they put in energy drinks , and why you may not be able to believe what the labels specifically say. our report from nbc's tom costello who has been reporting on the story for some time.

>> reporter: the headlines this week have been full of warnings about the caffeine levels in those high energy drinks. now, consumer reports has tested 27 products and found that five of the cans that list caffeine actually had caffeine levels at least 25% higher than what their levels indicated. and 11 of the products don't specify their caffeine levels at all, since they're considered a dietary supplement , they're not required to.

>> it is important to understand what you're drinking and if that information is not even available on the product, that is a problem.

>> reporter: among the drinks that don't list the caffeine levels, monster, last year, a teen died after cardiac arrest after drinking two of them in 24 hours , roughly five times the amount recommended for teens. the official cause of death , the toxic amounts of caffeine. while she did have an underlying heart defect, her mom is suing monster.

>> she is all i think about, i visit the cemetery every day.

>> reporter: monster says they don't believe their products are responsible for any death, and is unaware of any death caused by their products. but the fda confirmed that anise is one of five deaths that could be linked to energy drinks . monster points out the drink contains less caffeine than many high energy drinks, but as problems have a rose, er's are reporting overdoses.

>> it is about body weight, a certain amount of that drug could have a different effect than in a large person, an adult.

>> reporter: with kids in mind, congress is talking about requiring this drink producer to disclose their real amounts of caffeine. tom costello.