PHOENIX, AZ. — A new study has shown that consistently drinking energy drinks can raise the risk for an abnormal heart rhythm and increase blood pressure, according to CBS News. People who have heart problems should be especially cautious.

This research was presented at a meeting of the American Heart Association in Phoenix, Arizona by the University of the Pacific and David Grant Medical Center.

The study included 27 healthy volunteers between the ages of 18 and 40 who drank either two cans of an energy drink, or the same amount of a drink that contained panax ginseng (an ingredient in the energy drink), or a placebo beverage once a day, every six days, for three weeks.

The people who drank the energy drink had a statistically significant increase in a marker of abnormal heart rhythm risk known as the QTc interval, the researchers reported. The same study participants also experienced a slight rise in blood pressure. The effects persisted for two hours after the energy drink was downed.

“While we wait for more data, some consumers should exercise caution and not blindly follow the buzz,” says Sachin Shah, an associate professor of pharmacy practice at Pacific’s Thomas J. Long School of Pharmacy and Health Sciences.

Energy drinks have been linked with sudden death in extreme cases. The Center for Science in the Public Interest, a consumer health advocacy group, reports 34 deaths that may have been associated with energy drinks.