Consuming energy drinks may increase blood pressure and modify the heart rhythms of healthy humans, according to new research.

The finding, presented yesterday at a meeting of the American Heart Association in Phoenix, adds to growing concern over energy drinks that combine ingredients like caffeine, guarana and ginseng into a potent stimulant.

Researchers tested 27 healthy adults under age 40 in the small study. Participants who consumed two energy drinks saw a statistically significant increase in abnormal heart behavior and a rise in blood pressure when compared to a control group given a placebo. Both of these conditions lasted two hours.

The new research is far from the first study to caution that energy drinks may lead to adverse health effects. A 2015 study in the journal JAMA found that energy drinks raised blood pressure and caused a stress hormone in young people. Researchers behind the new study recommended that consumers, particularly young people, await further research before regularly drinking energy drinks.

This article originally appeared on Time.com.