Caffeine overdose is very real: See if you're drinking too much coffee

According to the Mayo Clinic, 400 mg of caffeine is our daily limit. Find out if you're putting your health at risk

Published November 13, 2015 8:15AM (EST)

  (<a href=''>DonNichols</a> via <a href=''>iStock</a>/Salon)
(DonNichols via iStock/Salon)

This article originally appeared on AlterNet.

AlterNet Americans drink a lot of coffee. In fact, the U.S. has the highest coffee consumption in the world, followed by the world's leading coffee producer, Brazil. Recent data show that American consumers spend an average of $21.32 on coffee per week.

It makes sense that coffee represents a fairly sizeable chunk of Americans' weekly spending, as caffeine has helped power the modern economy. "For most of human existence, your pattern of sleeping and wakefulness was basically a matter of the sun and the season," explains Charles Czeisler, a neuroscientist and sleep expert at Harvard Medical School. "When the nature of work changed from a schedule built around the sun to an indoor job timed by a clock, humans had to adapt. The widespread use of caffeinated food and drink — in combination with the invention of electric light — allowed people to cope with a work schedule set by the clock, not by daylight or the natural sleep cycle."

While the majority of Americans' caffeine intake comes from coffee, tea and soft drinks are also a main source. A Penn State study published last year found that 85 percent of the U.S. population consumes at least one caffeinated beverage per day.

Some of the report's other key findings:

  • The mean daily caffeine intake for all ages was 165mg.
  • Caffeine intake was highest in consumers aged 50-64 years.
  • The 90th percentile intake was 380mg/day for all ages.
  • Caffeine intakes from beverages are slightly higher than they were over a decade ago.
  • Energy drinks, energy shots and chocolate beverages contribute little to caffeine intakes.

If you're an average American, caffeine is a part of your daily life. But can you overdose on caffeine? Well, you can overdose on drugs, and caffeine is a drug, so the answer must be yes. But knowing exactly how much caffeine is required to cause an overdose is a little more complicated.

A central nervous system stimulant, caffeine is the world's most widely consumed psychoactive drug. Technically, it is part of a class of drugs known as methylated xanthines, which includes theophylline, a bronchodilator, and Trental, a drug used to treat muscle pain resulting from peripheral artery disease.

According to Mayo Clinic, the safe daily limit of caffeine for healthy adults is 400mg, which amounts to about 4-5 cups of coffee, 10 cans of soda or two "energy shot" drinks. (Ten cans of soda does sound high, but note that this is only considering caffeine — not sugar — intake. A can of soda typically contains 30-70mg of caffeine, while a cup of black coffee contains 260mg.)

In fact, the Penn State report's authors note several health benefits of caffeine, such as "weight loss, improved glucose tolerance and lower risk of type II diabetes, reduced risk for incidence of Parkinson’s disease and improvement in Parkinson’s symptoms, and reduced risk for cancer."

But regular caffeine intake can pose a variety of health issues as well. And these issues could become more common as caffeine is increasingly becoming an ingredient in a wide array of foods, drinks and over-the-counter drugs.


image: FDA

In 2013, the U.S. Food and Drug Administration said it would begin investigating the safety of caffeine in food products. The decision was a response to a worrying trend: caffeine being added to a growing number of food products. In fact, the agency made the announcement just as Wrigley's (a subsidiary of U.S. food giant Mars) was promoting a new pack of gum, each piece containing the same amount of caffeine as half a cup of coffee.

Have we become so addicted to caffeine that we need it delivered via chewing gum? While the American addiction to caffeine is well-established, most people will probably be surprised to know the growing list of food items that now come with added caffeine, from gum, jellybeans and marshmallows to waffles, syrup, sunflower seeds and water.

"Our concern is about caffeine appearing in a range of new products, including ones that may be attractive and readily available to children and adolescents, without careful consideration of their cumulative impact," said Michael R. Taylor, an FDA deputy commissioner. "The proliferation of these products in the marketplace is very disturbing to us."

The American Academy of Pediatrics discourages any caffeine intake by children and adolescents, while the Mayo Clinic says adolescents should have no more than 100mg of caffeine a day. In a 2011 clinical report, AAP outlined how sports and energy drinks — some of which contain more than 500mg of caffeine, the equivalent of 14 cans of soda — are being "heavily marketed to children and adolescents." The problem is that many parents have no idea.

"There is a lot of confusion about sports drinks and energy drinks, and adolescents are often unaware of the differences in these products," said Marcie Beth Schneider, a member of the AAP Committee on Nutrition and co-author of the report. "Some kids are drinking energy drinks, containing large amounts of caffeine, when their goal is simply to rehydrate after exercise. This means they are ingesting large amounts of caffeine and other stimulants, which can be dangerous."

The chart below shows the amount of caffeine found in a serving size of some common sources of caffeine, according to the Center for Science in the Public Interest:

The Mayo Clinic warns that people who drink more than four cups of coffee a day may feel a range of side effects, including insomnia, nervousness, restlessness, irritability, stomach upset, fast heartbeat and muscle tremors.

How sensitive you are to caffeine depends on a number of factors. According to Mayo:

How you react to caffeine may be determined in part by how much caffeine you're used to drinking. People who don't regularly drink caffeine tend to be more sensitive to its negative effects. Other factors may include body mass, age, medication use and health conditions such as anxiety disorders. Research also suggests that men may be more susceptible to the effects of caffeine than are women.

In addition, certain medications and supplements can also interact with the caffeine in your body. Some antiobiotics, like Cipro and Noroxin, can inhibit the breakdown of caffeine in the body, so you feel its effects longer. Theophylline, a breathing medication that opens up bronchial airwaves, has caffeine-like effects, and taking it with caffeine can cause nausea, vomiting and heart palpitations. Echinacea, an herbal supplement, may increase the concentration of caffeine in the blood.

To help consumers figure out how much caffeine is too much, Caffeine Informer designed a Caffeine Calculator:

Based on this calculator, it would be pretty hard to actually die from drinking caffeine. A 150-pound person would need to consume more than 62 cups of brewed coffee to get a fatal dosage. Still, you can experience symptoms of an overdose with a much smaller amount. Ingest between 400-600mg of caffeine and you could start experiencing unwanted side effects. According to theNational Institutes of Health, symptoms of caffeine overdose in adults may include trouble breathing or sleeping, rapid or irregular heartbeart, changes in alertness, confusion, convulsions, diarrhea, dizziness, fever, increased thirst or urination, vomiting and even hallucinations.

"You know you’ve overdosed if you’re feeling tremors or shaking throughout your body, which are the signs preceding the more life-threatening side effects," writes Samantha Olson of the health website Medical Daily. "The overdose happens when the body's central nervous system is thrown into a state of over-stimulation called caffeine intoxication. They body will actually expel the caffeine when it signals to itself it has had too much, just as the body would try to get rid of an alcohol overdose."

While the chances of a real caffeine overdose may not be great, caffeine dependence is more common. And like any dependence, there is a dark side.

"Caffeine helps people try to wrest control away from the human circadian rhythm that is hardwired in all of us," says neuroscientist Czeisler. "On the other hand, there is a heavy, heavy price that has been paid for all this extra wakefulness." He points out that without the conventional eight hours of sleep per night, the body will lose functionality — physically, mentally or emotionally. "As a society, we are tremendously sleep-deprived."

Czeisler describes the vicious cycle caffeine dependence creates: "The principal reason that caffeine is used around the world is to promote wakefulness. But the principal reason that people need that crutch is inadequate sleep. Think about that: We use caffeine to make up for a sleep deficit that is largely the result of using caffeine."

By Reynard Loki

Reynard Loki is a senior writing fellow and the editor and chief correspondent for Earth | Food | Life, a project of the Independent Media Institute. He previously served as the environment, food and animal rights editor at AlterNet and as a reporter for Justmeans/3BL Media covering sustainability and corporate social responsibility. He was named one of FilterBuy’s Top 50 Health & Environmental Journalists to Follow in 2016. His work has been published by Salon, Truthout,, EcoWatch and Truthdig, among others.

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