Although the amount of caffeine you get from one tea bag depends on steeping time, tea generally has less caffeine than coffee. Drinking five 8-ounce servings of tea per day is equivalent to drinking three 8-ounce servings of coffee, which has about 250 milligrams of caffeine, and is considered moderate caffeine consumption, according to MedlinePlus. Excessive caffeine consumption may cause upset stomach, nervousness and other side effects.
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In a study published in the October 2008 issue of the "Journal of Analytical Toxicology," 20 different tea products were brewed under a variety of conditions including different serving sizes and steep times. Researchers determined that caffeine concentrations in white, green and black teas ranged from 14 to 61 milligrams per serving. Both 6-ounce and 8-ounce servings contained roughly the same amount of caffeine per ounce, but caffeine content rose significantly with longer steeping time. Their findings indicate that even decaffeinated teas contain some caffeine, providing 12 milligrams or less per serving. However, herbal teas, such as peppermint and chamomile varieties, are generally caffeine-free.