The shots are highly caffeinated. The company won't disclose the exact amount, but Consumer Reports recently said they contain about 215 milligrams of caffeine.
An average cup of coffee can have from 80 to 150 milligrams, depending how it's made.
In the past four years, the FDA has received 90 complaints mentioning 5-hour Energy.
Nearly three dozen of them mentioned serious or life-threatening situations, such as heart attacks or convulsions.
Living Essentials, the distributor of 5-hour Energy, has maintained its products are safe when used as directed.
The report comes just a few weeks after the FDA said it was investigating five deaths mentioning Monster Energy, another popular energy drink.
Last year, the federal Substance Abuse and Mental Health Services Administration said there were more than 13,000 emergency room visits tied to energy drinks.
New York's Attorney General is investigating the producers of several high-caffeine energy drinks.
Some of the "energy boosters" are sold as beverages, while others are sold as dietary supplements, complicating FDA oversight of them.
