What Does Too Much Caffeine Do To Your Body? We Break Down 14 Popular Drinks, and How They Affect You

Caffeine is having a moment, and not for the best reasons. The drug has been linked to two deaths after it showed up in large quantities in a since-discontinued lemonade offering from chain bakery Panera Bread, and has even come under fire from lawmakers for appearing in energy drinks marketed towards by children. 

But despite all the negative attention, caffeine is still a popular element in plenty of products Americans consume on a regular basis. Case in point: Nearly 70% of U.S. adults said in a recent survey that they had a cup of coffee within the previous 24 hours — the highest number of daily coffee drinkers reported in the past two decades. Americans also eat about 10 pounds of chocolate a year, and there are plenty of other less obvious sources of caffeine we’re tossing back. 

Doctors say it’s important to be aware of what exactly it is you’re consuming when you have caffeinated products, as well as why you don’t want to go overboard. Here’s how caffeine impacts your body, along with exactly how much is in a range of popular products, from a shot of espresso to a can of Red Bull.

How does caffeine impact the body?

“Caffeine reduces the effects of adenosine, a signal that makes you feel sleepy, by blocking the adenosine receptors,” explains Rob M. van Dam, Ph.D., nutrition researcher and professor in the departments of Exercise and Nutrition Sciences and Epidemiology, Milken School of Public Health, at The George Washington University. This means caffeine stimulates your central nervous system, causing you to feel more awake and energetic than you would feel otherwise.

But caffeine is also a diuretic (meaning, it can cause you to pee more), increases the release of acid in your stomach, raises your blood pressure, and can interfere with the absorption of calcium in your body, per MedlinePlus. Caffeine reaches its peak level in your blood after an hour of consuming it, although you can feel the effects for up to six hours. 

Caffeine doesn’t impact everyone the same way. “If someone has ADHD, they might feel sleepy after caffeine,” says Jamie Alan, Ph.D., Pharm.D., an associate professor of pharmacology and toxicology at Michigan State University. She also points out that some people may also be more sensitive to the effects of caffeine than others.

The opposite can also be true, too, especially if you continue to use caffeine over time. The adenosine receptors in your body become less sensitive to caffeine as you continuously expose them to the drug, says Alan. As a result, you can build up a tolerance for caffeine over time.

Do all caffeine sources impact your body the same way?

It’s generally assumed by doctors that all caffeine sources impact your body the same way. “It doesn’t matter how you consume caffeine — eating or drinking — the effect is the same,” says Alan. 

However, van Dam notes that emerging research shows some components in coffee may partly inhibit the effects of caffeine, although more studies are needed to explore these relationships further. “Still, it is helpful to keep track of the total amount of caffeine consumed during the day from all sources to avoid consuming too much,” he says. 

These are some of the most popular caffeine sources that you may come across on a regular basis, and how much caffeine each contains.

But there are also super-charged products that have hit the market.

Of course, caffeine shows up in some foods, too. Dark chocolate (70% to 85%), for example, contains more than 22 milligrams of caffeine per ounce, according to the U.S. Department of Agriculture (USDA). Given that many people eat more than an ounce of chocolate at a time, you can have a significant amount of caffeine from dark chocolate without realizing it. 

How much caffeine is too much?

This is a surprisingly tricky question to answer. Most adults can safely have up to 400 milligrams of caffeine a day, according to the Food and Drug Administration (FDA). “That is similar to four to five 8-fluid ounce cups of coffee,” says van Dam. “However, the speed with which caffeine is metabolized in the body differs substantially from person to person.”

Caffeine recommendations are significantly lower for pregnant people, with the American College of Obstetricians and Gynecologists (ACOG) suggesting having no more than 200 milligrams per day for expectant moms. People with certain heart and cardiovascular conditions may also have lower caffeine thresholds, says Alan.

Signs you’ve had too much caffeine

You’ll usually develop uncomfortable symptoms if you have too much caffeine. Those can include, per the FDA:

• Trouble sleeping
• Jitters
• Anxiousness
• Elevated heart rate
• Upset stomach
• Nausea
• Headache
• Feeling unhappy
  

“Very large doses can cause seizures, hallucinations, and agitation,” says Alan. 

If you feel like your heart rate is too fast or it seems like it has an abnormal rhythm, Alan recommends seeking medical attention. But if you feel mostly OK after having too much caffeine, van Dam says you should be fine to ride it out. “Typically, waiting it out and reducing caffeine intake in the future is sufficient,” he says. 

“You can also take an antacid to settle your stomach or eat something bland, like oatmeal or a banana,” says Alan. Taking a walk or doing light exercise may also help reduce the effects of caffeine, she points out. And, of course, doing your best to have less caffeine.