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On October 23, 2012, The New York Times reported that the U.S. Food and Drug Administration (FDA) is investigating reports of five deaths that may be related to a popular energy drink called Monster Energy. The investigation is only in its early stages. While it's far too soon to implicate Monster Energy in these tragic events, it's a good time to take a look at these products.

Sports drinks such as Gatorade and PowerAde have been popular with athletes for decades. They contain electrolytes and carbohydrates. Athletes use them to replace fluids lost during exercise. Although it's not clear that sports drinks are actually better than plain water, they are safe.

Like sports drinks, energy drinks are sold in gyms, health clubs and supermarkets. Energy drinks are most popular among adolescents and young adults. And they sure are popular. In 2006, energy drinks racked up sales of $5.4 billion in the United States alone. But don't confuse them with sports drinks.

Caffeine is the key ingredient in energy drinks. Because so many of us get caffeine in coffee, tea and cola drinks, many people assume energy drinks are safe. And it is true that coffee is safe:

Many studies have reported that coffee does not increase the risk of heart attacks or sustained high blood pressure.
Other studies raise the possibility that coffee may even provide some protection against a variety of illnesses ranging from gallstones to colon cancer.

Unfortunately, medical research on coffee does not apply to energy drinks. Here's why:

Most energy drinks have much more caffeine (50 to over 500 milligrams a serving) than an average cup of java (75 to 150 milligrams a cup) or a typical 12 ounce cola drink (35 to 50 milligrams).
People drink hot coffee slowly. But energy drinks often go down fast, delivering a big jolt of caffeine to the blood and heart. That's an even bigger worry for the newest wrinkle: energy "shots" that can pack a large amount of caffeine into just an ounce or two.
Besides caffeine, energy drinks have many other ingredients that may or may not contribute to health problems. These include:
- Guarana – This is touted as a natural ingredient because it’s derived from a rainforest vine. Natural or not, it contains caffeine and other stimulants, such as theobromine and theophylline.
- Sugar – Many energy drinks are highly sweetened. Added sugars contribute to obesity and other health risks.
- Amino acids (the building blocks of proteins) and vitamins – They sound good and they are safe, but they don't provide either energy or health benefits.
- Artificial coloring and flavoring; chemical preservatives

Ingredients with unfamiliar names may sound scary, but that doesn't mean they're dangerous. Or, for that matter, helpful.

Since energy drinks are so popular, doctors should know if they are friend or foe, but they don't. A big reason for the lack of information is that energy drinks slip through the regulatory cracks. Most energy drinks are sold as "dietary supplements." The FDA can monitor and regulate medicine and food, but not dietary supplements. It's ironic, especially since the FDA is able to limit a 12-ounce cola drink to 71 mg caffeine.

So what do we know at this point?

According to government figures, more than 12,000 emergency department visits were linked to energy drinks in 2009. This is a big increase over previous years.
A handful of sudden deaths, heart attacks and seizures have occurred after drinking energy drinks. These anecdotes are worrisome, but they do not prove that highly-caffeinated energy drinks actually caused these events.
Energy drinks have also been linked to problem and risky behaviors, especially when they are combined with alcohol.

We need more research. Scientists in Australia recently investigated one type of energy drink by giving about 8 ounces to 30 healthy volunteers; most were young men. The drink only boosted blood pressure a small amount (about 3 mm Hg). And it did not increase heart rate. But it had just 80 mg of caffeine. Even so, it increased platelet stickiness and decreased the ability of blood vessels to widen normally. These changes were not seen in 20 volunteers who received only carbonated water.

In theory, these changes could increase the risk of the blood clots and narrow arteries that trigger most heart attacks.

These relatively small, brief changes do not necessarily translate into serious health problems. We need much more study to know if energy drinks are harmful. Until then, patients with cardiovascular disease should be cautious. Healthy young people should use common sense and listen to their bodies to see if their energy drinks trigger warning symptoms.

My best advice will have to rely on two old standbys: moderation in all things and buyer beware.

Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.

Energy Drinks -- Use Caution