How Much Caffeine is Safe?

Caffeine is a stimulant that revs up the nervous system, raises blood pressure and stimulates the heart. Caffeine is a drug, and like other drugs and medications, you can get too much caffeine, although you might not know it the way some early risers guzzle umpteen cups of coffee to wake up. How much caffeine is safe?

How Much Caffeine is Safe?

According to the Prescriber’s Letter, a guide for physicians, the average adult who has no medical problems can safely tolerate up to 400 milligrams of caffeine per day. This sounds like a lot until you consider that a single cup of brewed coffee has up to 120 milligrams of caffeine. Thus, 3 ½ cups of coffee would be the limit for adults who aren’t getting caffeine from other sources.

The problem is most people get caffeine from beverages such as tea, soft drinks, coffee and even some medications, although the amounts of caffeine in these sources is lower. Then there’s the problem of energy drinks. Some energy drinks have caffeine contents of up to 300 milligrams. Drink a single serving of an energy drink and a cup of coffee in the same day, and you’re over the recommended limit.

What Are the Effects of Too Much Caffeine?

Every organ system in the body is affected by too much caffeine. Most people are familiar with the shakiness, jitters, anxiety, hyperactivity and insomnia a few cups of coffee bring on. Too much caffeine also causes nausea, flushing and headache. The heart speeds up and some people experience irregular heart rhythms and premature contractions of the heart. When caffeine levels are very high, some people become very agitated and experience hallucination or seizures. There’s a good reason why caffeine is classified as a drug.

When a person gets too much caffeine, other things happen behind the scenes. Overindulging in caffeine causes levels of hormones called catecholamines, including adrenalin, to increase in the bloodstream. This leads to an increase in blood pressure, more production of glucose by the liver and changes in the digestive tract including increased secretion of stomach acid.  No wonder doctors urge people with conditions such as stomach ulcers, irritable bowel syndrome, high blood pressure, heart disease and diabetes to watch how much caffeine they take in.

How Much Caffeine is Safe: The Bottom Line?

Most healthy adults can tolerate up to 400 milligrams of caffeine per day, but sensitivity to caffeine varies. Some people experience unpleasant symptoms at much lower doses, especially if they’re not regular coffee drinkers. People who have heart disease, peptic ulcer disease, digestive issues, high blood pressure or diabetes should talk to their doctor before consuming caffeine. Tea and instant coffee are usually significantly lower in caffeine than brewed coffee, so consider switching to these if you’re trying to cut back.


Prescriber’s Letter. January 2011. Volume 18, No.l “Caffeine Intoxication and Addiction”

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