While they do boost your level of alertness, energy drinks have also been known to cause spikes in heart rate and blood pressure, dehydration, and digestive issues, according to the National Center for Complementary and Integrative Health.

Now, there’s another mark against these kinds of drinks: They may even mess with how your blood vessels function, according to new, preliminary research from a small study presented at this year’s American Heart Association’s Scientific Sessions.

In the study out of McGovern Medical School at UTHealth in Houston, Texas, researchers tested the endothelial function-or how well the membrane of cells lining the heart and blood vessels work to pump blood to your heart-of 44 healthy medical students in their 20s. Then, they had participants drink a 24-ounce Monster energy drink in one minute. Finally, the researchers tests their endothelial function once again 90 minutes later.

The results? On average, the participants’ blood vessel dilation decreased from 5.1 percent in diameter to 2.8 percent in diameter after consuming the can of Monster.

“This may result in reduced blood flow in various parts of the body, which might be problematic if someone is exercising-when they need extra blood flow,” lead study author John P. Higgins, M.D., M.B.A., sports cardiologist at McGovern Medical School at UTHealth, told Runner’s World. 

And while Higgins and his colleagues aren’t 100 percent sure why energy drinks might cause blood vessel constriction, they suspect it’s because of the combination of ingredients they contain, such as artificial sweeteners, caffeine, sodium, and taurine.

So if you find your eyes drooping during that afternoon slump or you need an energy boost before that track workout.