How Much Coffee Is Too Much Coffee?

Q: I routinely drink three or four cups of coffee per day, but often wonder if this is too much. Should I consider cutting back?

Coffee can be many things: a morning ritual, a cultural tradition, a productivity hack and even a health drink. Studies suggest, for instance, that coffee drinkers live longer and have lower risks of Type 2 diabetes, Parkinson’s disease, cardiovascular conditions and some cancers.

“Overall, coffee does more good than bad,” said Rob van Dam, a professor of exercise and nutrition sciences at the Milken Institute School of Public Health at George Washington University.

But between your breakfast brew, lunchtime latte and afternoon espresso, is it possible to have too much? And if so, how can you tell?

We asked experts to give us the unfiltered truth.

The consequences of overdoing it

Coffee contains thousands of chemical compounds, many of which may influence health, said Marilyn Cornelis, an associate professor of preventive medicine at Northwestern University Feinberg School of Medicine.

But coffee is also the largest source of caffeine for people in the United States, and that’s where most of the risks associated with coffee consumption come from, she said.

Having too much caffeine can cause a racing heart, jitteriness, anxiousness, nausea or trouble sleeping, said Jennifer Temple, a professor of exercise and nutrition sciences at the University at Buffalo.

It can also lead to headaches, acid reflux and, at high enough doses, even tremors or vomiting, said Dr. Adrienne Hughes, a medical toxicologist and an assistant professor of emergency medicine at Oregon Health and Science University.

But “most people are kind of well tuned with their response to caffeine,” Dr. Cornelis said, and when they begin to experience even mild symptoms of having too much, they cut back.

As such, it’s rare to experience dangerous side effects from drinking coffee, Dr. Hughes said. Caffeine overdoses typically result from taking in too much caffeine from concentrated forms, such as powders or supplements, in a short period of time, she said. And in most cases, you would need to consume at least 10,000 milligrams of caffeine — or the equivalent of about 50 to 100 cups of coffee, depending on the strength — for it to be potentially fatal, Dr. Hughes said.

Caffeine can cause a short-term increase in your blood pressure and heart rate, particularly if you don’t consume it regularly, she said. But this isn’t usually harmful. Studies show that habitual coffee drinking does not seem to raise blood pressure or the risk of an abnormal heart rhythm in the long run.

That said, if you’re prone to abnormal heart rhythms, or if you notice palpitations after having caffeine, you may be more sensitive to its effects and should not consume more than you’re used to, or ingest large doses from concentrated sources, like supplements or energy shots, Dr. Hughes said.

And having too much caffeine while pregnant is associated with an increased risk of miscarriage, Dr. van Dam said.

Know your limits

Most adults can safely consume 400 milligrams of caffeine — or the amount in about four eight-ounce cups of brewed coffee or six espresso shots — per day, according to the Food and Drug Administration. If you’re pregnant, the American College of Obstetricians and Gynecologists recommends no more than 200 milligrams.

Keep in mind that cup sizes and coffee strengths can vary. A typical eight-ounce cup has about 80 to 100 milligrams, according to the F.D.A. But at Starbucks, a “tall” (12 ounce) medium-roast brew contains around 235 milligrams of caffeine — about the same amount as a triple shot of espresso.

Caffeine can also be found in certain teas, sodas, dark chocolates, headache medications and some energy and sport supplements.

That being said, the 400 milligram guideline is reasonable for most adults, Dr. van Dam said. It also fits in with the research on how much you should consume to reap the health benefits while avoiding unpleasant side effects. Two to four cups per day is “kind of a sweet spot,” he said.

But people break down caffeine at different rates, Dr. van Dam said; 400 milligrams may feel like way too much for some, while others can routinely have more without any side effects.

Depending on your genetics, Dr. Cornelis said, it could take anywhere from two to 10 hours to clear half of a dose of caffeine from your blood. If you fall on the longer end of that spectrum, a midafternoon espresso may lead to trouble sleeping, whereas if you metabolize caffeine faster, you may not be bothered.

Smoking tobacco can also speed up your rate of caffeine metabolism significantly, which is why those who smoke may need to consume more caffeine to feel alert. And being pregnant or taking oral contraceptives can slow it down, Dr. van Dam said.

At the end of the day, “you just kind of have to listen to your body,” Dr. Temple said. “If you’re starting to feel nauseous or jittery or anxious, maybe cut back,” she said. “If it’s affecting your sleep, cut back.”