How much caffeine is dangerous? Here's what to know before reaching for another cup.

Whether we like it or not, the legal stimulant drug known as caffeine is a big part of our lives. We grab coffee on our way to work, refill our mugs at work and maybe grab an espresso martini after work. 

As the saying “everything in moderation,” dictates, there are healthy and unhealthy ways to get your caffeine fix. The right amount of coffee is linked to longevity, a stronger liver and lower chances of Alzheimer’s and Parkinson’s diseases, strokes and colon cancer, Johns Hopkins Medicine writes.

But there is such a thing as too much of a “good” thing.

How much caffeine is dangerous?

According to registered dietician Jordan Hill, the recommended limit for caffeine intake is about 400 milligrams per day. Still, Hill recommends 300 milligrams per day for adults, especially those who may be more sensitive to the side effects of caffeine.

An 8-ounce cup of coffee has just under 100 milligrams of coffee in it, so you should avoid that fifth cup of joe.

Coffee is not the only caffeinated substance — many types of tea, soda, energy drinks or bars, supplements and even chocolate contain caffeine. 

“Each of these items have different, varying amounts of caffeine in them, so if we're consuming them throughout the day, it could be very easy to go above that 300 milligram recommendation,” Hill says.

And what happens if you go above 400 milligrams? The potential for a number of side effects, according to Hill:

  • Headaches
  • Insomnia
  • Nervousness or anxiety
  • Irritability
  • Rapid heartbeat
  • Muscle tremors

Long-term over consumption may exacerbate these effects, and heavy caffeine drinkers could experience high blood pressure, ongoing gastrointestinal issues and, in rare cases, death. 

Caffeine is technically a drug; a stimulant. This means it speeds up the central nervous system and boosts energy levels. Caffeine is absorbed within 45 minutes of consuming, and stays in the blood anywhere between 90 minutes to nine and a half hours. This is also dependent on how much food is consumed, smoking (which speeds up the breakdown) or pregnancy and oral contraceptives (which slows it down). 

“We can build up a tolerance to it, which just means we require more caffeine to feel the same effects,” Hill says, pointing to short-term effects like alertness and increased productivity. “It might take more caffeine to feel those things, but at the same time, as that amount of caffeine goes up, so does the risk for side effects.”

Concerned about your caffeine intake? Hill recommends these tips to reduce your coffee consumption:

    • Switch between caffeinated and decaf coffee
  • Try a half decaf-half regular coffee
  • Transition to tea, which has less caffeine than a cup of coffee
  • Alternate coffee with water, which may quench your thirst by hydrating rather than reaching for another cup

How much caffeine can kids have?

The recommendation for kids ages 11 and younger is zero caffeine and less than 100 milligrams per day for kids ages 12 to 17, Hill says.

It’s not just coffee — parents should keep an eye out for caffeine in soda, chocolate, over-the-counter medications and even coffee-flavored foods like ice cream and candy. 

The biggest worry with children and caffeine is sleep disruption.

“That's going to impact their learning abilities the following day, they're going to be sleepy, they're not going to be as alert," Hill says. "It'll interfere with regular development."

Can you drink coffee while pregnant?

Drinking less than 200 milligrams of coffee per day is generally okay during pregnancy, Hill advises.

Caffeine is believed to cause blood vessels in the uterus and placenta to constrict, reducing the blood supply to the fetus. A 2021 study found pregnant people who consumed less than 200 milligrams of caffeine per day gave birth to smaller babies. 

Drinking a low to moderate amount of caffeine does not lead to an increased risk of gestational diabetes, preeclampsia or hypertension for pregnant people, researchers at the University of Pennsylvania found. A study even found that drinking up to 100 milligrams of caffeine per day correlated with a 47% reduction in diabetes risk. 

How much caffeine is in coffee?

According to Mayo Clinic, here’s approximately how much caffeine is in these popular 8 ounce drinks:

  • Brewed coffee: 96 milligrams
  • Brewed decaf coffee: 2 milligrams
  • Instant coffee: 62 milligrams
  • Instant decaf coffee: 2 milligrams
  • Black tea: 47 milligrams
  • Black decaf tea: 2 milligrams
  • Green tea: 28 milligrams
  • Bottled tea: 19 milligrams
  • Cola: 22 milligrams
  • Root beer: 0 milligrams
  • Citrus soda: 0 milligrams
  • Energy drink: 71.9 milligrams
  • Energy shot: 215 milligrams

Espresso shots have about 64 milligrams of caffeine, and decaf espresso shots are entirely caffeine-free.