What medical experts really want caffeine drinkers to know
Caffeine offers some real health benefits—but not if you go overboard. Here’s how coffee, energy drinks, and other caffeine products can affect your health.
America’s most popular drug, by a wide margin, is caffeine. A 2025 survey published in Food and Toxicology found that almost 70 percent of Americans consumed at least one caffeinated drink per day.
But caffeine isn’t just a cup of joe anymore. It’s available in gels, powders, gums, and pouches; there’s even caffeinated beef jerky. There has never been more variety in the delivery mechanisms and flavors at a caffeine consumer’s disposal.
The Food and Drug Administration suggests consuming no more than 400 milligrams of caffeine per day. An 8-ounce cup of brewed coffee typically contains about 95 milligrams of caffeine, while many popular energy drinks contain around 100 to 200 milligrams of caffeine per 12 ounces. In single servings, these doses aren't much of an issue for most, but the problem often starts when people start to overconsume.
(You actually can consume too much caffeine. Here are the risks.)
While caffeine does offer a number of health benefits, it can quickly bring on side effects at higher doses. Here’s what you should know about the positives and negatives of the stimulant, and who should be particularly careful about their consumption.
What’s happening in your body when you consume caffeine
Caffeine is a naturally occurring compound found in coffee, tea, and yerba mate, and the active ingredient in thousands of pre-workout supplements and energy drinks.
When consumed, caffeine blocks the absorption of the compound adenosine in the brain. Adenosine accrues while we are awake, and serves many functions in the body. When adenosine binds to its receptors, it promotes sleepiness, helping regulate our circadian rhythm. During restful sleep, the brain clears adenosine, leaving you feeling well-rested and alert upon waking. But caffeine, alcohol, and certain sleeping disorders can disrupt this process.
Caffeine blocks adenosine receptors, preventing adenosine from binding to these sites and sending the sleepy bat signal. Blocking the adenosine receptors provides a boost to other neurotransmitters as well—specifically dopamine, adrenaline, and epinephrine.
“That’s why you see the effects of caffeine on mood, energy, focus, and concentration,” says Robert Cowan, a neurologist and director of headache research at Stanford University.
How long caffeine remains in the body—and keeps you from getting a good night’s sleep—is highly variable from person to person. The general guideline, Cowan notes, is having no more than 400 milligrams per day and stopping consumption after 2 p.m.
(Coffee naps might be the weirdest—and smartest—way to recharge.)
Though the boosts from caffeine can be a great benefit, “the brain is not easily fooled,” Cowan warns. It quickly assumes, after regular usage, that caffeine is part of the body’s normal functioning. So when a regular caffeine user stops cold turkey, the brain will assume something is wrong and send a signal via headache, irritability, and fatigue.
How caffeine helps your body
Caffeine holds a number of health benefits depending on how it’s consumed. Energy drinks, for example, lack the additional compounds that teas and coffees contain—like polyphenols and antioxidants—that provide health benefits.
(Can energy drinks really boost your metabolism? Here’s what the science says.)
“When we're talking about the health benefits [of caffeine], we're really talking about coffee [and tea],” says Michael Fredericson, a sports medicine physician and professor at Stanford University. Even without the caffeine, coffee and tea pack powerful potential benefits. Studies and meta-analyses show that consumption of decaffeinated coffee is associated with lower rates of all-cause mortality, cardiovascular mortality, type 2 diabetes, and liver cancer.
Surprisingly, one study from the UK found that ground and instant—but not decaf—coffee, were associated with reduced arrhythmia, or irregular heartbeat.
When it comes to the world of sport and performance, caffeine is unparalleled.
“I don't think that there's a supplement that is as consistent as caffeine in improving exercise performance,” says Bryan Saunders, a researcher at University of São Paulo's Faculty of Medicine. In his research, Saunders has found that even the expectation of consuming caffeine, before consuming a placebo, improved performance nearly as much as caffeine.
Caffeine can boost focus while dulling the perception of pain and effort, making it an ideal performance compound. “You can work harder without feeling you’re working as hard,” Saunders says, which is particularly useful for endurance athletes.
The World Anti-Doping Agency signaled proof of caffeine’s power: Up until 2004, the organization held the compound on its banned substances list—though an athlete would’ve had to consume numerous back-to-back cups of coffee to exceed the 12 micrograms per milliliter of urine threshold.
The general recommendation—with exceptions—for exercise performance from the International Society of Sports Nutrition is three to six milligrams of caffeine per kilogram of body mass. For a 180-pound person, for example, that would be 250 to 490 milligrams of caffeine, which is slightly higher than the FDA’s daily recommendation.
Caffeine might also improve reaction time and attention to detail, Fredericson says. But too much can cause negative side effects like rapid heartbeat (known as tachycardia), jitteriness, anxiety, and difficulty sleeping.
“It’s a fine line,” Fredericson says, between benefits and side effects.
When to be careful about caffeine
Certain groups of people need to exercise additional caution about caffeine use.
It’s recommended that those who are pregnant limit their caffeine consumption to a maximum of 200 milligrams per day, according to the American College of Obstetricians and Gynecologists. Higher amounts can increase the risk of miscarriage and birth defects.
People with cardiac issues should also exercise caution with their caffeine consumption, says Cowan, as well as those with impaired kidney function or liver issues.
Anxiety, tremor, difficulty falling asleep, muddle-headedness, and flight of thought can all be signs of too much caffeine. Inconsistent caffeine consumption can also trigger headaches—particularly in those who suffer from migraine and are more sensitive to caffeine. At the same time, light caffeine users who feel a headache coming on can sometimes knock it out with a cup of coffee, or even a Diet Coke. The small amounts of caffeine in these beverages helps constrict blood vessels and makes medicine more effective.
(Can drinking Coke help with migraines? Science says yes—at least for some.)
“It’s the old ‘too much water and you drown’ kind of argument,” Cowan says of the benefits and risks of caffeine.
Caffeine can increase the absorption of other medications, which is sometimes why it’s included in prescription medications and over-the-counter drugs like Excedrin. It’s also the reason, Cowan says, that someone taking heart medications should be careful about their caffeine consumption, as it can affect the amount of medication absorbed in the bloodstream.
Fredericson, along with the American Academy of Pediatrics (AAP), does not recommend energy drinks for adolescents. But 30 to 50 percent of adolescents drink them anyways, according to the Centers for Disease Control and Prevention.
Caffeine, in general, can disrupt brain development in adolescence. The AAP cites concerns of “anxiety, hyperactivity, inattention, sensation-seeking, and poor decision-making,” in addition to a detrimental effect on sleep. Energy drinks have massive doses of caffeine, which can compound overall stress.
“That’s the last thing you need at that stage of your life,” Fredericson says. “These kids are already way too stressed, so that’s my biggest concern.”
Improperly dosed and timed caffeine disrupts sleep in adults as well, which can lead to many of the health issues that careful caffeine consumption can help. Sleep problems, Fredericson says, can increase risk for cardiovascular disease, diabetes, and Alzheimer’s.
Cowan’s guidance is to exercise moderation and consistency with caffeine. In addition to the daily caffeine limit, the FDA also recommends stopping consumption by 2 p.m. People who metabolize caffeine slower should stop earlier in the day to avoid disrupting their sleep, while fast metabolizers might have no problem with a post-dinner espresso.
Everyone is different, but two to four cups a day is Fredericson’s ballpark recommendation.
“You just need to find out what works for your body.”
