The rumor: It's possible to get caffeine poisoning

As he was driving down an Ohio freeway minutes after swallowing five Magnum 357 caffeine pills, Christian Brenner started to vibrate -- and the cars in his rearview mirror did as well. Fortunately, Brenner pulled over and walked around in an effort to try and come down.

Today, he swears off caffeine, even coffee -- the mental aftereffect of what he says was straight-up caffeine poisoning.

The verdict: Yes, you can OD on caffeine. The trick is to know your body, pay attention to what else you've ingested and do your homework on energy drinks

Caffeine acts as a stimulant in humans. It can be found in the seeds, leaves and fruit of plants like coffee or kola nuts.

"Safe doses of caffeine are usually quoted at around 200 to 300 milligrams, or two to four cups of coffee per day," says Dr. David Seres, associate professor of clinical medicine at Columbia University.

There have been plenty of reports that say caffeine is beneficial. Some studies call it a potential protector from diseases such as Parkinson's, and even some forms of cancer.

But those 357 Magnum Pills that Brenner ate contain 200 milligrams of caffeine each, which means he downed around 1,000 milligrams of caffeine in one big literal gulp.

Take note: Energy drinks like Red Bull usually contain around 80 milligrams of caffeine in an eight-ounce can. Some of the bigger cans (such as a 16-ounce Monster) have up to 240 milligrams. Meanwhile, a 16-ounce cup of coffee (think a venti at Starbucks) packs upwards of 300 milligrams.

Barbara Crouch, executive director at the Utah Poison Control Center, says that unlike coffee drinkers, energy drink consumers (especially young people) like to chug down not just one, but two or three of the peppy beverages to get a good jolt on before a hardcore workout, soccer practice or maybe to enhance a night of dancing.

"When you pound down more than one energy drink verses sipping a cup of coffee, you're not metabolizing it the same way," she says, adding that factors like size, age, sex, drug interactions, hydration levels and the amount of food in the stomach can mean different outcomes for different people when on a caffeine binge. "Yes, there is absolutely such a thing as caffeine poisoning, and the dose essentially makes the poison," she says.

But Crouch has a bigger bone to pick with the makers of energy drinks: She says that many of them aren't being fully forthcoming about ingredients. Seres points out that many "natural" additives -- such as guarana, taurine and so-called "Siberian ginseng" -- haven't been fully tested.

"Energy drinks contain other 'natural' ingredients, which may have additional amounts of caffeine," says Seres. "They're also likely to contain herbs with stimulatory effects not tested for safety or interactions with prescription drugs, and other potentially pharmacologically active substances."

But James Coughlin, a food, nutritional, chemical and toxicology safety expert in Los Angeles who consults for the American Beverage Association (the industry group that represents energy drink companies), disputes that.

"The caffeine contained in the guarana of an energy drink is only around one milligram, versus the 80 milligrams of synthetic caffeine added by a beverage company such as Red Bull," he says. "The lethal dose of caffeine is 10 to 20 grams of pure powder caffeine, so if you were going to try and kill yourself with caffeine, you'd probably drown in the liquid first if you did it with coffee -- and even more so with an energy drink."

Coughlin calls the very idea that beverage companies are sneaking caffeine into energy drinks through other ingredients a total myth.

Still, it'd be hard to deny headlines claiming that there have been increased energy drink-related visits to emergency rooms. One highly cited 2011 report from the Substance Abuse and Mental Health Services Administration stated that energy drink-related emergency-department visits went from 10,068 visits in 2007 to 20,783 visits in 2011.

All the press about energy drinks led the Federal Drug Administration to say it's taking a fresh look at caffeinated food -- and that it plans to hone in on how energy drinks impact young people.

"We are contracting with the Institute of Medicine to conduct a public meeting to obtain additional scientific information and expert input on caffeine and are actively reaching out to the food industry and health care practitioners to discuss concerns about caffeine in conventional foods and dietary supplements," says FDA spokesperson Teresa Eisenman.

Crouch, however, cautions that people should monitor caffeine intake from other sources as well.

"So you have that cup of coffee, but lo and behold you decide to get an extra-dark bar of chocolate," she says. "Or you drink a soda. Or maybe you do take an allergy pill or a dietary supplement." Truth be told, sometimes people miss the fine print on labels about stimulant properties in all these products.