The energy drinks that seem to fill the coolers of every convenience store and checkout line carry some risks that go beyond the jitters of drinking too many.
Experts have been cautioning teens and other adults for years against stoking up on multiple cans of the stuff before sporting events, for instance, because it can actually increase the risk of dehydration and contribute to an elevated heart rate even before exercise begins.
Now new studies suggest that the drinks' caffeine boost can do even more damage to people with high blood pressure and those who mix buzz juice with booze.
First the blood pressure problem.
Researchers in Detroit had 15 young adults (average age 26) skip caffeine from any source for two days. Then, on the third day, after getting a baseline measure of blood pressure, heart rate and other vital signs, the researchers had them drink two cans of energy drink with 80 milligrams of caffeine each, about the same found in a cup of coffee.
The subjects continued the routine for about a week. Over that time, the heart rates increased by five to seven beats a minute and systolic blood pressure went up by about 10 percent.
"This occurred while participants were sitting in chairs watching movies," as opposed to physical exertion, said James Kalus, the research pharmacist who led the study. It was presented Tuesday before the American Heart Association's annual scientific meeting in Orlando, Fla.
In fact, while the drinks are often marketed around images of extreme-sports competitions, marathons or study days, researchers are finding that many high-school and college students are using the energy drinks to keep them awake for longer alcoholic binges.
Another study shows that college students who drink booze mixed with energy drinks are twice as likely to be hurt or injured than those who did their drinking without the aid of the boosters.
This was among the findings of Wake Forest University researchers that were presented to the American Public Health Association's annual meeting in Washington this week.
The Wake Forest team also found that those students who mix are twice as likely to require medical attention or to ride with an intoxicated driver than students who just drank alcohol.
Additionally, those who mixed energy and alcoholic drinks were more than twice as likely to take advantage of someone else sexually, and almost twice as likely to be taken advantage of, according to the study. It was based on a Web survey of nearly 4,300 college students from 10 universities.
"We knew, from speaking with students and researching blogs and Web sites, that college students mix these drinks and alcohol in order to drink more and to drink longer," said Dr. Mary Claire O'Brien, an associate professor of emergency medicine who led the study.
"But we were surprised that the risk of serious and potentially deadly consequences is so much higher for those who mixed energy drinks with alcohol, even when we adjusted for the amount of alcohol."
Overall, 24 percent of the students said they mixed the stimulant drinks with alcohol in at least one drinking session in the past 30 days, with the practice more common among white males, athletes and fraternity members.
Just as the time-honored practice of pouring coffee into an inebriated partygoer produces a "wide-awake drunk," O'Brien says younger party goers may not realize how impaired they are because of the stimulant effect.
"Only the symptoms of drunkenness are reduced, but not the drunkenness. They can't tell if they're drunk and they can't tell if someone else is drunk. So they get hurt, or they hurt someone else."