How much caffeine is safe for adults?

by Mark Miller February 15, 2016 4 min read

How much caffeine is safe for adults?

Study after study has found recently that moderate amounts of caffeine are not harmful. So healthy adults need not deny themselves coffee, tea or other products unless the caffeine interferes with sleep.

Sages and philosophers from various world traditions have counseled “Everything in moderation,” and, stated another way, “Nothing in excess.” These aphorisms apply to caffeine, too, because too much of this otherwise beneficial chemical can cause insomnia, nervousness, muscle tremors and stomach upset.

Excess caffeine can also cause irritability, headaches restlessness, excessive urination and fast heartbeat. These side effects come with what calls heavy caffeine use of 500 to 600 milligrams per day.

How much caffeine is safe?

Take the news about excess caffeine in moderation, though, because with the correct amount it can alleviate fatigue and make a healthy adult feel more awake, focused and concentrated. And it has other benefits, including enhancing the effectiveness of pain relievers, reducing inflammation and alleviating migraines and other types of headaches.

And coffee does not cause extra heartbeats, a study that came out in January 2016 advises. “Whether or not they have the jitters, most regular coffee drinkers can at least be assured the caffeine probably isn’t giving them extra heartbeats, at least according to an analysis based on a cohort from the prospective Cardiovascular Health Study (CHS),” says an article at

But just exactly how much caffeine is safe? About 300 to 400 milligrams of caffeine are right for an adult, about 100 mg for adolescents and none for children, says Mayo.

The National Sleep Foundation states:

There is no nutritional need for caffeine in the diet. Moderate caffeine intake, however, is not associated with any recognized health risk. Three 8 oz. cups of coffee (250 milligrams of caffeine) per day is considered a moderate amount of caffeine. Six or more 8 oz. cups of coffee per day is considered excessive intake of caffeine. … Once in the body, caffeine will persist for several hours: it takes about 6 hours for one half of the caffeine to be eliminated.

The European Food Safety Authority did a study of how much caffeine is OK. It found what Mayo and the National Sleep Foundation reported—that about 400 mg per day “do not raise safety concerns.” Also, about 200 mg in one dose right before exercise is OK.

How much caffeine do products contain?

It is hard to know just how much caffeine you are getting, though. The amounts of caffeine in various products vary widely, and estimates given by various agencies and websites also differ in the amount of caffeine in each product.

Caffeine amounts in coffee vary so much that Viter Energy blog published an entire article exploring that beverage. Eight ounces of the dark elixir vary anywhere from 100 to 270 mg of caffeine, depending on the variety of beans it’s made from and the type of brewing process. Brewed coffee averages about 163 mg in 8 ounces. reportsthat there are 400 mg of caffeine are in five shots of espresso, about 11 12-ounce colas, five 8-ounce Red Bulls, one Starbucks 20-ounce brewed coffee and two 5 Hour Energy Shots.

The USDA reports black tea has about 72 mg of caffeine in 12 ounces, Extra Strength Excedrin pills have 65 mg per tablet and Midol Complete gelcaps have 60 mg. Also, sodas vary from about 35 to 64 mg per can. A 41 gram bar of Hershey’s Special Dark Chocolate bar has 18 mg, and nine Hershey’s Kisses have about 9 mg of caffeine.


How much caffeine is safe

Black tea has about 72 mg of tea in 12 ounces. The cocoa in the chocolate cake too has small amounts of caffeine. (Photo by Nicubunu/Wikimedia Commons)

Correct amounts vary by person

But there are other factors besides caffeine content when considering how much is safe for adults, including a person’s own metabolism. A certain amount of caffeine can be good for one person but wrong for another person. Some people are more sensitive to caffeine’s effects, and the effects vary by age, weight and other factors.

Mayo clinic says:

How you react to caffeine may be determined in part by how much caffeine you’re used to drinking. People who don’t regularly drink caffeine tend to be more sensitive to its negative effects. Other factors may include body mass, age, medication use and health conditions such as anxiety disorders. Research also suggests that men may be more susceptible to the effects of caffeine than are women.
People who don’t habitually drink coffee or take caffeine in tea, soda, energy drinks , drugs, chocolate or other candy may be the most prone to restlessness and even sleep loss if they have some in the late afternoon or in the evening.

To function at their best, most adults need about seven to eight hours of sleep every night. Too much caffeine can cause sleep loss and eventual chronic sleep deprivation, a longer-term problem than losing one night of sleep.

Beware sleep deprivation

Sleep deprivation decreases alertness and performance, impairs memory and thinking processes, puts stress on relationships and can cause occupational injuries or automobile accidents.

And it can be a vicious cycle. People who are losing sleep often drink coffee to feel alert, which makes it harder to fall asleep and stay asleep at night.

But the news about caffeine and sleep is not all bad: “Because caffeine is a stimulant, most people use it after waking up in the morning or to remain alert during the day,” says the National Sleep Foundation. “While it is important to note that caffeine cannot replace sleep, it can temporarily make us feel more alert by blocking sleep-inducing chemicals in the brain and increasing adrenaline production.”

If you stick to no more than 400 mg, or three to four 8-ounce servings of coffee per day, you should be fine, and your performance and alertness may be enhanced. Many medical experts advise people not to take caffeine later than mid or late afternoon so sleep is not disrupted.

Mark Miller
Mark Miller

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