There may be some new clues on why energy drinks can pose a bigger health risk than other caffeinated drinks.
Some people may think energy drinks are just like super-strong coffee.
But, experts are noticing a difference.
A recent study shows they affect the heart differently than regular caffeine alone.
In a small test with young people, energy drinks raised blood pressure, and increased part of the heart beat called the Q-T interval.
It is the time it take heart ventricles to generate a beat. When these intervals are too long or too short, it can cause the heart to beat abnormally.
But a drink with caffeine and sugar alone didn't have that effect.
Researchers divided 18 young participants into two groups. The first received 32 ounces of an energy drink that contained 108 grams (g) of sugar, 320 milligrams (mg) of caffeine, and various other compounds.
The second had a control drink with the same amount of caffeine, as well as lime juice and cherry syrup.
The increase in the Q-T interval was small, and doctors say by itself it's probably not harmful.
However, energy drinks combined with alcohol, which can also cause arrhythmias, could disrupt the heart's rhythm enough to spark problems.
The study was reported by the American Heart Association.