Caffeine: How much is too much?

Caffeine has its perks, but it can pose problems too. Find out how much is too much and if you need to curb your consumption.

By Mayo Clinic Staff

If you rely on caffeine to wake you up and keep you going, you aren't alone. Caffeine is used by millions of people every day to increase wakefulness, alleviate fatigue, and improve concentration and focus.

How much is too much?

Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two "energy shot" drinks.

Although caffeine use may be safe for adults, it's not a good idea for children. And adolescents should limit themselves to no more than 100 mg of caffeine a day.

Even among adults, heavy caffeine use can cause unpleasant side effects. And caffeine may not be a good choice for people who are highly sensitive to its effects or who take certain medications.

Read on to see if you may need to limit or even end your caffeine routine.

You drink 4 or more cups a day

Heavy daily caffeine use — more than 500 to 600 mg a day — may cause side effects such as:

  • Insomnia
  • Nervousness
  • Restlessness
  • Irritability
  • Stomach upset
  • Fast heartbeat
  • Muscle tremors

Even a little makes you jittery

Some people are more sensitive to caffeine than are others. If you're susceptible to the effects of caffeine, just small amounts — even one cup of coffee or tea — may prompt unwanted effects, such as restlessness and sleep problems.

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.

Apr. 14, 2014 See more In-depth