Whether you drink to ward off a 3 p.m. energy drop or fuel a lethargic workout, there's a burgeoning should-I-or-shouldn't-I debate surrounding energy drinks that's impossible to ignore.

So what's the impact of slugging one back? An 8-12 ounce energy drink has 72-150 mg of caffeine, which isn't necessarily problematic. After all, studies have found that up to four cups of coffee a day—which could top off around 400 mg—can actually have positive health benefits like lowering your risk of diabetes, upping your mood, and decreasing the risk of cardiovascular diseases.

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But a large energy drink bottle can flood your body with up to 294 mg of caffeine in one sitting. Look at a label and you'll also notice that the average Monster contains way more than your morning cup o' joe, namely sugar and other ingredients like taurine, ephedrine, guarana, and ginseng. All those "extras" act as stimulants, enhancing caffeine and sugar's effects, and throwing your body into overdrive.

More troubling? The efficacy—and health risks—of those additives are largely unknown, said Maria Pagano, M.S. R.D., C.S.C.S. and Equinox Tier 4 coach.

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So before you reach for an artificial pick-me-up, Pagano explains what's going on under the hood while you're sipping.

Your brain: Caffeine blocks the effects of adenosine, a brain chemical that helps you sleep (which is why too much can lead to insomnia). But it also fires off neurons in your brain to keep you alert, causing your pituitary gland to initiate the "fight or flight" response. That's your body's natural reaction to prepare for a threat.

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Your bloodstream: After the "fight or flight" response is activated, your pituitary gland releases adrenaline, which sends a signal to your liver to pump more glucose (a.k.a energy) into the bloodstream.

Your heart: Adrenaline makes your heart beat faster and your eyes dilate, effects that can last longer than you might like. In fact, a recent German study found that healthy people who drank caffeine and taurine-packed energy drinks saw increased heart contraction rates up to an hour later.

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Back to your brain: With more glucose in your bloodstream and your body in fight-or-flight mode, the increased dopamine levels trick your brain in to believing that you have more energy than you really do.

Your skin: Sweat excessively while exercising and you'll lose water and electrolytes—both of which sports drinks work to replace. Reach for an energy drink after that, though, and you'll only dehydrate yourself more.

Your body: Too much caffeine can produce a diuretic effect, which can also mean dehydration. If you overdo it, you could feel jittery, anxious, and irritable from too much of the stimulant and a lack of water.

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