Caffeine: How much is too much?

If you rely on caffeine to wake you up and keep you going, you aren't alone. Caffeine stimulates the central nervous system, alleviating fatigue and increasing wakefulness.
When to consider cutting back

For most people, moderate doses of caffeine — 200 to 300 milligrams (mg), or about two to four cups of brewed coffee a day — aren't harmful. But some circumstances may warrant limiting or even ending your caffeine routine. Read on to see if any of these apply to you.
'Grande' is your middle name

Though moderate caffeine intake isn't likely to cause harm, too much can noticeably affect your health. Heavy daily caffeine use — more than 500 to 600 mg a day, or about four to seven cups of coffee — can cause:

Insomnia
Nervousness
Restlessness
Irritability
Nausea or other gastrointestinal problems
Fast or irregular heartbeat
Muscle tremors
Headaches
Anxiety

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 anxiety, restlessness, irritability and sleep problems. How you react to caffeine may be determined in part by how much caffeine you're used to drinking. So, people who don't regularly consume caffeine tend to be more sensitive to its negative effects. Other factors may include body mass, age, smoking habits, drug or hormone use, stress and health conditions such as anxiety disorders. Sex may even play a role: Research suggests that men are more susceptible to caffeine than are women.