Energy drinks are supposed to do just what the name implies -- give you an extra burst of energy. As it turns out, most of that "energy" comes from two main ingredients: sugar and caffeine. A typical energy drink can contain up to 80 milligrams of caffeine (about the same amount as a cup of coffee). By comparison, a 2006 study found that the average 12-ounce soda contains 18 to 48 mg of caffeine.

Other than caffeine levels, how do energy drinks differ from sodas and sports drinks? Soft drinks are mainly water, sugar and flavoring. They don't do anything for your body; they're just supposed to taste good. Sports drinks are designed to replenish fluids lost during activity. They typically contain water, electrolytes and sugar. Energy drinks have added caffeine and other ingredients that their manufacturers say increase stamina and "boost" performance. They're designed for college and graduate students, athletes and anyone else who wants an extra energy kick.

Energy drinks became popular in Asia long before they reached the United States. In 1962, Japanese pharmaceutical company, Taisho, released its Lipovitan D drink. It was designed to help employees work hard well into the night. Lipovitan D contains taurine, the same ingredient found in many of today's energy drinks. The very first "energy" drink to reach the United States wasn't really an energy drink at all -- it was more of a hyped-up soft drink called Jolt Cola®. The "jolt" in the cola was a lot of added sugar and caffeine. Introduced in the 1980s, Jolt Cola® quickly became a staple on college campuses.

Red Bull® Banned! Red Bull® may be the best selling energy drink in the United States, but it isn't so popular in other countries. In 2000, the French government decided to ban Red Bull after the brand was linked to the death of an 18-year-old Irish athlete. The teenager died after drinking four cans of Red Bull® at a game. French laws dictate the maximum amount of caffeine that companies can add to products, and Red Bull® exceeds that limit. Denmark and Norway have also banned the drink. Other countries, such as Canada, require the can to carry a warning label for pregnant women and children.

Energy Drink Ingredients
Here are some of the ingredients you may find in popular energy drinks and what they do in the body:

Ephedrine is a stimulant that works on the central nervous system. It is a common ingredient in weight-loss products and decongestants, but there have been concerns about its effects on the heart.
Taurine is a natural amino acid produced by the body that helps regulate heartbeat and muscle contractions. Many health experts aren't sure what effect it has as a drink additive.
Ginseng is a root believed by some to have several medicinal properties, including reducing stress and boosting energy levels.
B-vitamins can convert sugar to energy and improve muscle tone.
Guarana seed is a stimulant that comes from a small shrub native to Venezuela and Brazil.
Carnitine is an amino acid that plays a role in fatty acid metabolism.
Creatine is an organic acid that helps supply energy for muscle contractions.
Inositol is a member of the vitamin B complex (not a vitamin itself, because the human body can synthesize it) that helps relay messages within cells in the body.
Ginkgo biloba, which is made from the seeds of the ginkgo biloba tree, is thought to enhance memory.

Image © George Doyle

Looking at the ingredients, energy drinks appear to be part soft drink and part nutritional supplement. According to reviewers, the taste falls within the same range. People who have tried energy drinks have described the taste as ranging from "medicinal" to "molten Sweet Tart." Although the manufacturers claim that energy drinks can improve your endurance and performance, many health experts disagree. Any boost you get from drinking them, they say, is solely from the sugar and caffeine.

Caffeine works by blocking the effects of adenosine, a brain chemical involved in sleep. When caffeine blocks adenosine, it causes neurons in the brain to fire. Thinking the body is in an emergency, the pituitary gland initiates the body's "fight or flight" response by releasing adrenaline. This hormone makes the heart beat faster and the eyes dilate. It also causes the liver to release extra sugar into the bloodstream for energy. Caffeine affects the levels of dopamine, a chemical in the brain's pleasure center. All of these physical responses make you feel as though you have more energy.

Beyond the Energy Craze Image courtesy The Coca-Cola Company Diet Coke Plus® So you know that energy drinks like AMP®, Burn®, Full Throttle®, Jolt Cola®, Monster® and Red Bull® have been storming supermarket shelves. But what's next? Soda that packs a different kind of punch - one that's supposed to be good for you. Coke and Pepsi are both hitting the market with vitamin-fortified soft drinks in 2007. But they're not calling them "soft drinks." These new products are "sparkling beverages." The Coca-cola Company will debut Diet Coke Plus®, which will boast the good-for-you add-ons niacin, vitamins B6 and B12, magnesium and zinc. And Tava®, PepsiCo's new sparkling beverage, will be enhanced with B3, B6 and E, and chromium.

Energy drinks are generally safe, but like most things, you should drink them in moderation. Because caffeine is a stimulant -- consuming a lot of it can lead to heart palpitations, anxiety and insomnia. It also can make you feel jittery and irritable. Over time, caffeine can become addictive. It is also a diuretic; it causes the kidneys to remove extra fluid into the urine. That leaves less fluid in the body. So drinking an energy drink while you're exercising can be particularly dangerous. The combination of the diuretic effect and sweating can severely dehydrate you.

Other ingredients can also be problematic. For example, the stimulant ephedrine, an ingredient in many decongestants, can cause heart problems. In 2001, two California high school students fainted after ingesting energy drinks containing ephedrine. Because very little research has been done on the long-term health effects of consuming excess amounts of taurine and other ingredients in energy drinks, many health experts advise pregnant women and young children to avoid them.

And here you can see that the pituitary gland senses the increased neuron activity in the brain and releases adrenaline into the body. The adrenal glands pump adrenaline throughout the body, making the heart beat faster and the liver release extra sugar for energy.