Now, to a big health warning about the popular energy drink 5-hour energy. Federal officials say it may have been a factor in at least 13 deaths over the past 4 years. Abc's jim avila has the story.... See More
Now, to a big health warning about the popular energy drink 5-hour energy. Federal officials say it may have been a factor in at least 13 deaths over the past 4 years. Abc's jim avila has the story. Reporter: It's a small bottle, just two ounces. But packs a powerful caffeine punch, equal to two cups of coffee. Having one of those days? Tired. Groggy. Reporter:5-hour energy led the way in this new and growing segment of energy drinks. A stiff shot of caffeine and vitamins to jolt you away. Now, the federal government and the new york attorney general's office are investigating claims that it could do more than that. The fda has received reports of 13 deaths and 33 hospitalizations over the past 4 years, claiming 5-hour energy was involved. Now, someone wants to drink multiple cans, which is when we're really seeing a lot of the side effects with this, you're getting up to astronomical amounts. 30, 40 cups of coffee. Reporter: It's the second time in a month the fda has confirmed it's investigating claims that energy drinks are causing fatal reaction. In october, monster energy, another popular drink that contains even more caffeine, was linked to five deaths. The manufacturers point out, these are just claims. And there's no proven link between the drinks and the deaths. In a statement overnight, 5-hour energy said, the product is intended for busy adults. The company says its compact product contains as much caffeine as a cup of the premium coffee. The creator of 5-hour energy told abc news "nightline," when used as directed, the caffeine in his product does no harm. Water is good. But if you have too much, you drown. Reporter: The fda warning this morning, while there's no proven link between energy drinks and these reported deaths, you should check with your doctor before drinking them.
This transcript has been automatically generated and may not be 100% accurate.