Energy drinks sell you on increasing alertness, fighting fatigue, and improving reaction time. But we wondered: When you pop the top, what are you really pouring into your body?

Energy-drink companies are helping popularize exotic-sounding compounds that even scientists don’t yet fully understand. The approach has worked: In 2009, Americans spent $4.2 billion on these supposedly high-octane elixirs. But do these beverages really energize your body and sharpen your mind? Or should you can the energy drinks for good?

To help you separate the science from the marketing hype, we analyzed five key ingredients in the market’s most popular potions.



What Is It? An extract made from the root of the ginseng plant. Panax ginseng is the species most commonly used. The ginseng content in energy drinks typically ranges between 8 milligrams and 400 milligrams in 16 ounces.

Does It Work? Not if you’re hoping for energy to burn. A recent review in American Family Physician determined that ginseng doesn’t enhance physical performance. But there is an upside: It may boost your brainpower. Andrew Scholey, PhD, an herb and nutrition researcher at Australia’s Swinburne University, and his colleagues found that people who swallowed 200 milligrams of the extract an hour before taking a cognitive test scored significantly better than when they skipped the supplement. They also felt less mental fatigue. Ginseng may work by increasing the uptake of blood glucose by cells in the brain, says Scholey. However, the right amount is essential—only two of the eight major energy drinks we examined contained that optimal dose of at least 200 milligrams.

Is It Safe? Because the amount of ginseng in an energy drink is minimal, harmful effects are unlikely. And while there have been some reports of negative side effects from ginseng—diarrhea, for example—Scholey points out that those occurred in people taking 3 grams a day. One caution: If you’re on any medications, check with your doctor before knocking back an energy drink. Ginseng has been shown to impede blood-thinning drugs like warfarin.


A potential brain boost, but don’t expect any extra energy or physical prowess.



What Is It? A South American shrub. One seed has a caffeine content of 4 to 5 percent, while a coffee bean has 1 to 2 percent. The amount of guarana in a 16-ounce energy drink ranges from a minuscule 1.4 milligrams to as much as 300 milligrams.

Does It Work? Yes, if you don’t set the bar too high. A study in the journal Appetite reports that people who took 222 milligrams of guarana felt slightly less fatigued and were up to 30 milliseconds faster on a reaction-time test than those who popped a placebo. Some scientists attribute guarana’s effect solely to its caffeine content, but Scholey isn’t so sure. His team found energizing effects with doses just under 40 milligrams, which contains little caffeine. That means there’s probably something else in guarana that produces a stimulating effect on its own or that bolsters the effect of the caffeine, he says.

Is It Safe? Scientists at Florida’s Nova Southeastern University recently conducted tests and concluded that the amounts of guarana found in most energy drinks aren’t large enough to cause any adverse effects. That said, there’s still a question mark regarding the safety of higher levels, which could conceivably be consumed by downing a few energy drinks in a brief time span. For a sure pick-me-up, rely on these energy boosting foods instead.


Guarana may fight fatigue and improve reaction time.



What Is It? One of the most abundant amino acids in your brain, where it can act as a neurotransmitter—a chemical messenger that allows your cells to communicate with one another. You’ll find anywhere from 20 milligrams to 2,000 milligrams of taurine in most 16-ounce energy drinks.

Does It Work? Scientists aren’t sure, but it doesn’t seem likely. When taurine is dumped into your bloodstream—when you down a Red Bull, for instance—it can’t pass through the membranes that protect your brain, says Neil Harrison, PhD, a professor of pharmacology at Weill Cornell Medical College. But even if it could, Harrison’s research suggests that taurine might behave more like a sedative than a stimulant. When he and his team applied the amino acid to the brain tissue of rodents, they discovered that it mimicked
a neurotransmitter that slows brain activity.

Is It Safe? Taurine is probably fine in small doses, but chug too many energy drinks and the picture becomes less clear. According to a recent case report from St. Joseph’s Hospital in Phoenix, Arizona, three people had seizures after drinking two 24-ounce energy drinks in a short period of time. However, the researchers don’t know whether to blame the taurine or the caffeine. The fact is, there’s been little research on taurine consumption in humans, so it’s impossible to conclude whether it’s safe to consume in high doses.


It doesn’t appear to boost energy levels, and may actually deplete them.



What Is It? A chemical compound that stimulates your central nervous system. Most energy drinks contain between 140 and 170 milligrams of caffeine in a 15- or 16-ounce can.

Does It Work? Java junkies certainly think so. As for the science, an Austrian study showed that men who swallowed 100 milligrams of caffeine had a bigger boost in brain activity after 20 minutes than those who took a placebo. Plus, a new University of Chicago study found that a 200-milligram jolt made fatigued people feel twice as alert as noncaffeinated participants.

Is It Safe? The most caffeine-packed energy drink contains the equivalent in caffeine of about two 8-ounce cups of coffee. If downing that much joe doesn’t make you jittery, then quaffing a can shouldn’t pose a problem. Of course, if you combine that with other caffeinated beverages throughout the day, then the sum total stimulation could cause headaches, sleeplessness, or nausea. On the other hand, if you’re not a regular coffee or cola drinker and you battle high blood pressure, the occasional energy drink could be trouble. Researchers in Finland reported that the caffeine in 2 to 3 cups of coffee can cause blood pressure to spike by up to 14 points.


Caffeine can increase alertness and brain activity. It can also increase the jitters, so use wisely.



What Is It? Sugar. Sucrose, another ingredient you’ll often see on energy drink labels, is a combination of fructose (the natural sugar found in fruit) and glucose. Many energy drinks contain 50 to 60 grams of glucose or sucrose in a 16-ounce can.

Does It Work? Your body runs mainly on glucose, so topping off your tank with the sweet stuff should theoretically provide an instant boost. And in fact, a recent study in the Journal of Applied Physiology found that men who guzzled a 6 percent glucose drink were able to bicycle 22 minutes longer than those who went sans the extra sugar. Where glucose won’t help, however, is with the fog of fatigue from too little sleep. A 2006 British study determined that sleep-deprived people who drank liquid glucose exhibited slower reaction times and more sleepiness after 90 minutes than those who drank nothing.

Is It Safe? Dumping empty calories down your gullet is never a great idea, and some energy drinks contain nearly as much sugar as a 20-ounce soda. Then there’s the fact that a sudden infusion of glucose can cause your blood sugar and insulin levels to skyrocket, signaling your body to stop incinerating fat. A 2006 New Zealand study reveals that caffeine combined with even the 27 grams of sugar in, say, an 8.3-ounce Red Bull may be enough to temporarily inhibit your body’s ability to burn lard.


Our bodies run on glucose, but using sugar as your energy source is a recipe for obesity.


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