Caffeine is a stimulant, and anyone who has ever had one cup too many knows that overdoing it on the coffee can leave you jittery. But you may have heard about more serious issues caffeine might cause in large amounts, such as caffeine toxicity and nerve damage. Is there a link? How much is too much?
"There is evidence that caffeine affects the nervous system," says Seattle, Washington-based Ginger Hultin, MS, RDN, registered nutritionist dietitian and a spokesperson for the Academy of Nutrition and Dietetics. "I see no evidence that it commonly causes nerve damage, especially when consumed at normal doses."
While caffeine toxicity is a real threat, nerve damage is not specifically stated as a side effect in studies. In a June 2020 review in StatPearls, the authors note that complications of caffeine overdose include neurologic changes (among others) and could ultimately result in kidney injury, muscle tissue injury or heart attack. But they note that neurologic changes are transient and reported to resolve on their own as caffeine leaves your body.
A thorough examination of the toxicology profile of caffeine in a November 2018 review in Toxicology Reports found that high doses may cause muscle tissue damage, called "rhabdomyolysis," independent of any effect on nerves.
While your nerves may be clear of real damage, the other side effects of caffeine toxicity can be harmful, even life-threatening.
So, how much is too much? The U.S. Food & Drug Administration (FDA) says that at a level of about 1,200 milligrams of caffeine a day you may be putting yourself in danger. This level could be toxic and lead to serious health harms such as seizures (abnormal electrical signals in the brain, according to Columbia University). The FDA says highly concentrated products increase your risk of caffeine toxicity.
The Trouble With Caffeine
If you're a healthy adult, you should be able to tolerate as much as 400 milligrams of caffeine a day, according to the FDA. That's about 4 cups of coffee, depending on how and where the beans were grown, processed and prepared.
But Hultin says that some people may be more sensitive to the effects of caffeine than others due to genetics and certain health conditions. "Anyone who has cardiac issues, or is sensitive to stimulants of the nervous system, or is on other supplements or medications to help treat these types of issues should use a lot of caution when consuming caffeine," she says.
The U.S. National Library of Medicine (NLM) and FDA warn more caffeine than you can personally tolerate can cause a host of issues, such as:
- Rapid or abnormal heartbeat
Too much caffeine also can increase sympathetic nerve activity, part of the network that controls your involuntary responses such as sweating, Hultin says.
How Much Caffeine Is Safe?
An 8-ounce cup of coffee has about 80 to 100 milligrams of caffeine, while a similar-size cup of tea has about 30 to 50 milligrams, per the FDA.
Run the numbers to see how much you might be drinking per day. A 12-ounce can of soda with caffeine has about 35 to 45 milligrams, according to the NLM. What about energy drinks? Each one can add another 70 to 100 milligrams of caffeine to your day's total.
Caffeine is also in chocolate and some medications, especially those you might take for colds, per the NLM. Some dietary supplements have concentrated amounts of caffeine as well, according to the FDA.
Even some packaged foods might contain caffeine. Many voluntarily list how much caffeine is in them, the FDA says. "Read the labels to understand how much caffeine you're taking in and pay close attention to how it affects you," Hultin says.
When to Call Your Doctor
"Because caffeine can cause blood pressure to rise, if you struggle to maintain normal blood pressure, it would be smart to call your doctor if you're having symptoms of cardiac or nervous system problems," Hultin says. If you think the situation represents an emergency, don't hesitate to take action, she adds.
For more information, visit the U.S. Health Resources & Services Administration Poison Help or dial 800-222-1222.
Read more: 6 Surprising Signs You're Drinking Too Much Caffeine
- U.S. National Library of Medicine: “Caffeine”
- U.S. Food & Drug Administration: “Spilling the Beans: How Much Caffeine Is Too Much”
- Ginger Hultin, MS, RDN, registered dietitian nutritionist; founder, Champagne Nutrition; spokesperson, Academy of Nutrition and Dietetics; Seattle, Washington
- Columbia University: Department of Neurology: “Epilepsy and Seizures”
- StatPearls: “Caffeine Toxicity”
- Toxicology Reports: “The Clinical Toxicology of Caffeine: A Review and Case Study”
- U.S. Health Resources & Services Administration: “Poison Help”