This comes on the heels of another investigation looking at 'Monster' energy drinks and if they can be blamed for five deaths.
According to Consumer Reports, the amount of caffeine in Five Hour Energy is said to be 207 milligrams. That is equivalent to about two small cups of regular coffee.
Monster drinks are reported to have about 160 mg of caffeine, which is a little less, but many experts say these investigations may be more about the other ingredients.
Listed on the label of Five Hour Energy is Taurine. Scientists say it boosts the potency of caffeine, so comparing energy drinks to coffee isn't really fair.
"If you knew you were capable of drinking four cups of coffee over the morning, you probably would feel different than if you drank four energy drinks," said Dr. Marcie Schneider, an expert on adolescent medicine and nutrition.
The FDA will be looking into all the ingredients in these products and how they act together.
The founder of Five Hour Energy told Jim Avila of ABC News his product is safe when used as instructed.
But damage to their public image may be already done.
One runner spoke with Action News at the expo for the Philadelphia Marathon saying she used to occasionally drink a Five Hour Energy, but says that habit will change.
As a reminder, it is important to point at that just because there are reports of deaths and other problems, does not mean the energy drinks are to blame.
The FDA will have to look at all of the cases and how the products were used and by whom before making a determination.