Whether it’s endless cups of coffee during marathon Zoom sessions, energy drinks to power through the midday slump, or performance gels to fuel hard-charging workouts, it seems like most people can’t get through their day without a hit of caffeine. No wonder, according to an article in StatPearls, it's the most widely consumed psychoactive drug in the world.
As with many good things, too much caffeine can be problematic, and even deadly. While poisonings or deaths caused by caffeine are rare, they do happen. A study published in May 2018 in Nutrients identified 92 cases in which caffeine was found to be the sole cause of death, and noted that these cases were more common among infants, psychiatric patients, and athletes than in the general population.
One such case that received a lot of attention involved a UK-based trainer who died after consuming a caffeine powder supplement that delivered the equivalent of around 200 cups of coffee, the BBC reported in March 2022. (It appears he incorrectly measured the portion, resulting in a toxic dose of the stimulant.)
This very rare but troubling deadly outcome of caffeine exposure may leave you wondering if the amount of caffeine you are taking is safe.
Certainly, caffeine can be a safe part of daily life for most people. Current guidelines from the U.S. Food and Drug Association (FDA) suggest that up to 400 milligrams (mg) of caffeine a day is fine for healthy adults. That’s the equivalent of about four to five 8-ounce (oz) cups of coffee, although research has found that caffeine levels can vary depending on the beans used, how they were roasted, and how the coffee was brewed. A study published in February 2019 in Food Research International compared eight brewing methods and found that filtered coffee tends to have less caffeine per cup than other methods, while cold brew tends to have more.
The upper limit for safe coffee consumption is six cups a day, according to research published in March 2019 in the American Journal of Clinical Nutrition. Interestingly, the same study found that coffee drinkers had an 11 percent lower risk of cardiovascular disease than coffee nondrinkers, but it’s unclear whether that effect can be attributed to caffeine or other compounds in coffee.
Caffeine is lethal only at extremely high concentrations. For some perspective, a review of caffeine safety published in Frontiers in Psychiatry in May 2017 found that 10 mg of caffeine per kilogram (kg) of body weight is considered toxic and 150 mg/kg can be lethal. So, for someone who weighs 150 pounds, toxicity can start at around 700 mg and lethality at 10,000 mg.
The FDA has warned against concentrated caffeine powders, as there is a greater risk you'll consume more than the recommended amount and reach toxic or even deadly levels. The agency estimates that toxic effects, like seizures, can be observed with rapid consumption of around 1,200 mg of caffeine, or 0.15 tablespoons of pure caffeine. That fact makes the practice of “dry scooping” or consuming supplement powders directly from the container, without mixing with liquid first as directed — a practice made popular on TikTok and other social media platforms — especially dangerous. Since caffeine is present in many preworkout supplements, dry scooping can involve the ingestion of potentially dangerous amounts of caffeine.
Data collected between 2011 and 2012 and published in Nutrients in 2016 showed that, among caffeine consumers, the average daily intake was about 135 mg, and came from just three main sources: coffee, tea, and soft drinks. A typical 8 oz cup of coffee has 80 to 100 mg of caffeine, 8 oz of green or black tea has 30 to 50 mg, and 12 oz of caffeinated soft drink delivers 30 to 40 mg, according to other research.
But caffeine can now also be found in myriad other products in the supermarket, including ice cream, energy bars, breakfast cereals, chocolate bars, protein powders, and, of course, caloric and noncaloric energy drinks, in which caffeine levels can inch up to 300 mg per can. Recently, the Hostess brand introduced caffeinated doughnuts as a “tasty, energy-boosting, grab-and-go way to jump-start the day.” The caffeinated doughnuts contain 50 to 70 mg of caffeine (and around 300 calories) each. Caffeine is even a component of many over-the-counter pain relievers and prescription drugs. So an individual’s caffeine intake can really add up over the course of a day.
For most people, caffeine consumption is relatively safe at amounts typically obtained from drinks and foods, according to the Frontiers in Psychiatry study. But people do differ in their sensitivity to the stimulant depending on several factors, including genetic differences in the enzyme that metabolizes caffeine, past researchfound. In addition, there is evidence that women are less sensitive to the effects of caffeine than men are.
“What is too much for one person is completely fine for someone else,” says Marilyn Cornelis, PhD, an associate professor of preventive medicine at Northwestern University in Chicago who has conducted research on coffee consumption and caffeine metabolism. Some people may be more responsive to caffeine at lower doses and experience some unpleasant side effects.
Since too much caffeine looks different for everyone, look for these signs that it might be time to reconsider that extra engine-revving cup of coffee in the morning.
Caffeine is a stimulant, best known for promoting wakefulness and increasing feelings of energy. “Caffeine works by binding to the brain’s adenosine receptors,” says Dr. Cornelis. Adenosine is a molecule that activates feelings of calm and tiredness, and when caffeine blocks adenosine receptors in the brain, it can help you trade feelings of fatigue for those of alertness, research shows. This is generally a good thing if you need to perk up for a morning meeting, but for some people this extra arousal can spill over into feelings of anxiousness, irritability, and nervousness, Cornelis says.
Caffeine-induced anxiety disorder is one of four caffeine-related syndromes listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM), which is published by the American Psychiatric Association. High daily intakes of 1,000 mg or more per day have been reported to cause nervousness, jitteriness, and similar symptoms in most people, whereas more moderate intakes may lead to similar effects in caffeine-sensitive individuals. And if you already suffer from anxiety in noncaffeinated instances, then it may just make the condition worse.
If you notice that you often feel nervous, agitated or jittery after drinking a strong coffee or polishing off a caffeinated energy bar, it might be a good idea to look for other ways to boost energy levels, like taking a morning walk.
“Depending on the person, the amount consumed, and the timing of intake, caffeine can increase the time it takes to fall asleep and decrease the overall quality of your sleep,” says Cornelis. Tossing and turning at night can be an indication that caffeine has impacted your sleep cycle.
Caffeine concentrations peak in your blood up to about two hours after consumption, research shows, but some studies have found that it can stick around for as long as 9.5 hours, which could potentially interfere with your usual bedtime.
And even if you aren’t pounding espressos after lunch, you may still be getting a surprisingly high amount of caffeine later in the day from sources like dark chocolate and matcha lattes. Foods and beverages are not required by law to list how much caffeine they contain, so you may not even realize how much you’re getting.
Young adult women with higher caffeine intakes from sources including coffee and energy drinks were found to be more prone to poor sleep quality, according to a study published in April 2020 in Sleep Health. Since restorative sleep is so important for overall health, evaluate your caffeine intake, both the amount and timing, to make sure that it’s not keeping you wide-eyed at 2 a.m.
That skull crusher could be the result of a third cup of coffee. Caffeine-induced hyperexcitability of the central nervous system can contribute to migraine onset in certain people, particularly at high intakes, according to a study published in August 2019 study in the American Journal of Medicine.
For most people, consuming a moderate 200 mg of caffeine daily is fine, reports the National Headache Foundation, but the organization suggests that those who frequently suffer from headaches avoid daily caffeine use.
It’s worth noting that caffeine withdrawal can be an even bigger contributor to the onset of migraines, especially when there is an abrupt reduction in the amount, according to aa December 2019 report in Frontiers in Neurology. So it’s better to wean yourself off slowly if you realize you have a problem.
For some people, caffeine can cause tachycardia, an increase in heartbeat speed. “Caffeine-sensitive people or those with compromised heart functioning are at a higher risk of experiencing heart palpitations,” says Cornelis.
A high acute dose of caffeine for someone who is not a habitual user may also send the heart into overdrive. But, according to a study review in the November 2017 issue of Food and Chemical Toxicology, healthy adults who consume fewer than 400 mg of caffeine in a day will not typically experience meaningful adverse effects on heart rate.
Generally, any acute uptick in heart rate should subside fairly quickly once the caffeine gets through your system, but you may find the feeling is uncomfortable enough to make you reconsider how much you are taking in. Anyone with a diagnosed heart condition needs to be much more aware of this potential side effect of caffeine and speak with their physician.
There is a reason food manufacturers are pumping caffeine into everything, and coffee chains are brewing up turbo drinks: It makes consumers feel like they have superhero energy levels. As your body metabolizes the drug, however, you can face the opposite effect. With no more caffeine blocking the adenosine receptors in your brain, the sleep-inducing chemical can be released — and what’s more, research shows that your body may be extra sensitive to it.
So that tendency for 2 p.m. yawn fests and lower motivation to work could be chalked up to too much caffeine earlier in the day. Make note of how much caffeine you are consuming earlier in the morning and how you are feeling in the afternoon to see if there could be a correlation.
Your morning cup of joe could be making it more difficult for you to keep your hand out of the cookie jar, according to a study published in August 2017 in the Journal of Food Science. Researchers found that caffeine could temporarily affect taste buds and make food and drink seem less sweet — which could cause you to crave more sugar to get your fix. If you find that you’re jonesing for sweets close to the time when you are getting caffeine, and this is resulting in less than stellar dietary choices, it might be a good idea to cut back on the stimulant to see if it helps rebalance your taste perception. You may find that doughnut now tastes much too sweet, leaving you wanting it less.
There are 56 medications known to interact with caffeine, according to Drugs.com. Because caffeine consumption is at an all-time high, and prescription drug use is more prevalent than ever, the risk of negative caffeine and prescription drug interactions is increasing.
If you are taking prescription medications, or even over-the-counter options like acetaminophen, make your doctor aware of your caffeine exposure so they can advise appropriately on any possible pharmacokinetic interactions.
While research shows that small amounts of preworkout caffeine can give your fitness regimen a boost, too much can have the opposite effect. After a review of the existing literature, the International Society of Sports Nutrition (ISSN) officially took the position that supplementing with caffeine in moderation appears to have a positive impact on aerobic endurance and muscular endurance and strength, among other fitness-related benefits, according to a position paper published in January 2021 in the Journal of the International Society of Sports Nutrition. The paper identifies amounts of caffeine ranging from 2 to 6 mg per kilogram (kg) of body mass as beneficial, but also points out that very high doses of caffeine (9 mg/kg of body mass) are associated with a high incidence of side effects such as tachycardia and heart palpitations, anxiety, and headaches. So if you’re experiencing those or other side effects during or after your usual workout, you may want to cut back on the preworkout caffeine fix.
If your caffeine use is negatively affecting your health or lifestyle, it may be in your best interest to reduce your intake. While it may be tempting to go cold turkey, Cornelis cautions that doing so can cause withdrawal side effects. Research shows these include fatigue, nausea, flu-like symptoms, headaches, and mood disturbances. Unlike opioid or alcohol withdrawal, caffeine withdrawal is not considered dangerous, but it can certainly be unpleasant. “To make things easier on yourself, reduce caffeine gradually to limit or avoid the common withdrawal symptoms,” Cornelis advises. One way to do that: Cut your caffeine intake by 25 percent every week or so until you can keep it below the threshold where you are inviting caffeine-induced concerns.