5-Hour Energy Beware, energy shot devotees.

For many of us who march in the sleep-starved army that is the American workforce, it’s as critical to our survival as air, food, and bad reality TV: Caffeine. Beloved, energizing, career-preserving caffeine.

But here's a word of caution to you true overachievers: the slightly sweaty/foot-tapping/takenobreathsbetweenwords caffeine junkies. For you, coffee was the gateway drug -- to energy drinks and, later, to energy shots. Too much of a good thing may help shrink that massive work stack before the 5 p.m. whistle, but it also may kill you -- or just land you in the hospital.

Case in point: The 22-year-old woman who arrived at an emergency room complaining of upper abdominal pain, nausea, vomiting and a slight fever, according to the June 22 edition of the Journal of Medical Case Reports. A scan of her midsection was normal. She was sent home. She returned, however, even sicker, and bathed in a yellowish tint -- jaundice -- meaning her liver was failing. Doctors diagnosed the woman with acute hepatitis.

The staff checked her for viruses, alcohol and drugs. Nothing. Then the woman revealed a key part of her diet over the previous two weeks: 10 bottles of 5-Hour Energy per day.

Math time, lady: If the product indeed provides a five-hour boost, that two-week binge totaled 700 hours of “energy.” There are only 336 hours in two weeks. Must have been one hell of a deadline.

Doctors believe the woman overdosed on one ingredient: niacin -- also called vitamin B3 -- which can damage the liver when ingested in high amounts. She was successfully treated and discharged after her symptoms vanished.

Makers of 5-Hour Energy print recommendations on their labels: “Do not exceed two bottles” per day. The shots “contain caffeine comparable to a cup of … coffee,” they add. The drink’s sales pitch: “Zero sugar. Four calories. No waiting. No hassles.”

“Energy drinks are propped up by all sorts of sexy marketing, but they’re not as magical as the ads would have you think,” says TODAY nutritionist Joy Bauer. “The ‘lift’ they give you comes from caffeine -- nothing fancy there. … The high doses of B vitamins and amino acids they dump in are purely for glitz and glam -- they don’t actually help you instantly perk up.

“Energy shots offer a very concentrated dose of caffeine, which makes it difficult to stop when you feel like you’ve had too much, unlike if you’re slowly sipping a cup of coffee.”

But even coffee has its human limits, according to the website energyfiend.com -- which offers a macabre calculator to reveal the fatal dose of nearly any caffeinated beverage, based on body weight.

A 130-pound person, for example, would “be pushing up daises” after guzzling 151.67 cans of Mountain Dew, the site estimates. And for a 200-pound person, the site warns, “Gulp down 143.68 cups of Starbucks Tall Cafe Mocha and you’re history.”

In that case, hold the whipped cream.

Bill Briggs is a frequent contributor to msnbc.com and author of “The Third Miracle.”