It is possible that the combination of sugar, stimulants, and caffeine found in energy drinks can result in changes to the heart’s electrical system. This can contribute to an abnormal—and possibly dangerous—heart rhythm change. Additionally, energy drinks can increase blood pressure more than caffeine can alone.

A recent study (published in the Journal of the American Heart Association) looked at 18 healthy adults between the ages of 18 and 40 at a United States air base. The study was initiated by the military, which wanted to investigate the drink’s effects due to personnel consuming energy drinks regularly on base and while deployed. Half of the study participants were asked to drink 32 ounces of an energy drink containing herbal ingredients, 320 milligrams of caffeine, and 108 grams of sugar.

The other half of the participants were given a control drink containing carbonated water, cherry syrup, lime juice, and 320 milligrams of caffeine. The heart activity and blood pressure of the participants were monitored for up to six hours, and a follow-up was performed the next day. Six days later, the groups switched beverages and were studied again.

It was found that the energy drinks affected heart rhythm and elevated blood pressure for longer than the control drink.

The study’s lead researcher, Emily Fletcher (deputy pharmacy flight commander at David Grant U.S.A.F. Medical Center) stated that it is important for consumers to remember that drinking an energy drink is not the same as drinking soda or coffee. Energy drinks should only be consumed in moderation, and Fletcher went on to suggest that those with hypertension or cardiac disease avoid energy drinks altogether. They should also be avoided while participating in sports or exercise, when your blood pressure and heart rate are already affected.

Other professionals pointed out the limited scope of the study, and indicated that energy drinks are likely fine for healthy adults.

Patients are advised to talk to their doctors about the consumption of energy drinks and look for ways to safely increase energy, like exercise and sleep.