Caffeine is a drug many of us consume every day without thinking twice.
But what do we really know about it?
New research out this week shows caffeine not only keeps people alert but helps shift workers perform better and make fewer errors.
However, not everyone can handle large doses of caffeine, and figuring out where you're getting your biggest hit can be tricky.
Coffee is still the king of caffeine, but if that morning jolt of java isn't enough, the sky's the limit.
You can find everything from energy drinks to medication, gum and even cosmetics.
At Buzz Killer Espresso in Chicago's Wicker Park, coffee aficionados swear that it's mostly about the taste, not the kick.
"It's a mixed order - we expect that caffeine hit and that flavor and they go hand in hand," said Buzz Killer co-owner Stefan Hersh.
Most doctors say caffeine in moderation - about 200-300 milligrams daily - is fine. That comes to roughly two 12-ounce cups of coffee a day. Exceeding that among can result in jitteriness, insomnia, anxiety and a possible short spike in blood pressure.
Researchers at Johns Hopkins say that it takes as little as 100 milligrams a day to lead to dependence.
Monitoring caffeine intake can be tricky.
A 20-ounce cup of coffee at Starbucks has about 415 milligrams of caffeine, while the same cup at Dunkin' Donuts has about 224 milligrams of caffeine.
A person starting their day with a Starbucks, drinking a Pepsi in the afternoon and then popping two extra strength Excedrin tablets and ending their night with a Hershey's dark chocolate bar would rack up a whopping 519 milligrams of caffeine.
Throw an energy drink into the mix, and you could be adding up to an extra 300 milligrams.
Many times, people are not sure what they are consuming, and despite requests, the FDA does not require that caffeine be listed.
"It's been 12 years now, and the FDA has done nothing," said David Schardt, a nutritionist for the Center for Science in the Public Interest.
Several soda manufacturers are voluntarily including caffeine amounts on their nutrition labels.
Caffeine is a stimulant, working by temporarily changing the chemistry of the brain, which provides a mental and physical boost.
It blocks a brain chemical called adenosine. When that happens, dopamine, a feel-good chemical, and the stress hormone adrenaline are released.
Different people can metabolize and respond to caffeine in vastly different ways.
"People definitely underestimate the potency of the drug that is caffeine," said Dr. Harriet de Wit, a psychopharmacology professor at the University of Chicago Medical Center. "They think that they are drinking their coffee every day out of habit or just because they like the taste of it, but actually, there is a very strong psychoactive component that is improving their mood and improving their performance."
De Wit and her University of Chicago Medical Center colleagues discovered that about 20 percent of the population may have gene variations which can make them more anxious when caffeine is ingested or slow down the time it takes for caffeine to leave the body.
Lisa Viverito may be one of them. She has eliminated caffeine from her diet and says her migraines and depression are gone.
"The first two weeks, you go through withdrawal," said Viverito. "It's an addiction."
Dr. Martha Howard, a practitioner of integrative medicine, says people should consider their caffeine intake, no matter how small it is - especially if they are feeling agitated, anxious and having trouble sleeping.
"People can get a lot of caffeine and then they don't associate the symptoms with it," said Howard.
For those who seem to have no problems, there is probably no reason to avoid caffeine.
Many researchers say there is little evidence of serious health risks and growing evidence of health benefits, such as preventing diabetes, Parkinson's disease, Alzheimer's disease, liver disease, and even some cancers.
Tom MacDonald says caffeine affects him differently as he has gotten older. He is not giving it up, but he is cutting back.
"If I drink two to three cups of strong coffee, I'm just completely wired the rest of the day, so now I'm starting to mix caffeinated and decaf, or drinking more tea," said MacDonald.
Pregnant women are advised to avoid caffeine or at least limit consumption to about 200 milligrams a day.
There are no guidelines for teens yet, but concern is mounting that children are getting too much caffeine.
Center for Science in the Public Interest
American Dietetic Association
Buzz Killer Espresso
Chicago, Il. 60647