Some people get used to these negative side effects and find that they need more and more caffeine to bring on the stimulation they crave. Since caffeine is addictive, withdrawal often causes headache, irritability, insomnia and lack of concentration.

Caffeine in foods

Average caffeine concentration in common foods:

• Brewed coffee (5 ounces): 115 mg
• Diet Coke (12-ounce can): 41 mg
• Iced tea (12 ounces): 15 mg
• Brewed decaf coffee (5 ounces): 3 mg
• Two Excedrin: 130 mg
• Caffeinated water (8 ounces): 70 mg
• Brewed tea (5 ounces): 31 mg
• Espresso (1 ounce): 35 mg
• Chocolate candy bar (1 ounce): 20 mg

The amount necessary to cause changes in our body is 100 mg. Look at your mug of coffee: If it's 5 ounces or larger, you're using caffeine as a drug every time you take a sip. Children, being smaller, are affected by even lower doses of caffeine. Instead of blaming your child's erratic behavior on the sugar in soda, think about the caffeine instead.

How much is too much?

Most experts agree that moderate caffeine intake, 200-300 mg per day or about three cups of coffee, has no long-term health implications. Caffeine is excreted within a few hours and does not build up in our body. Pregnant women are advised to keep caffeine intake low to prevent any risk of pre-term delivery or spontaneous abortion. The American Cancer Society notes that no research connects caffeine consumption with cancer. Caffeine also does not cause cardiac problems, although sensitive individuals who experience increased heart rate from caffeine will want to steer clear of all products that contain it.