It's also mildly addictive. If you take in caffeine regularly, you're apt to feel lousy if you miss your fix. As drugs go, caffeine is relatively benign. But restrict caffeine if you have anxiety, insomnia, panic disorder, heart arrhythmias, tachycardias or palpitations, or if you're pregnant, Griffiths advises.
Some experts say avoiding caffeine can lower blood pressure.
Subjects showed faster response times on mental tests within minutes of drinking a cup of caffeinated tea, vs. decaf. In other British research, a cup of tea or coffee in the morning, early afternoon and early evening preserved alertness and good mental functioning all day, compared with plain water. More than half of regular caffeine users are apt to suffer withdrawal if they quit abruptly, says Griffiths. You can suffer after giving up just one cup of coffee a day. His new research also finds it takes only three days of taking in 300mg a day to get hooked.