Generally, a cup of brewed green tea contains less caffeine than coffee or black tea, although the exact amount depends on how each beverage is prepared. Caffeine levels can vary depending on the cultivar, harvest material, amount of tea used, water temperature, and steeping time. Using less tea, cooler water, and a shorter steep generally results in less caffeine being extracted into the cup.
If you want to reduce your caffeine intake, you can discard the first infusion. Caffeine dissolves readily in water, so the first infusion can contain a substantial amount of the tea’s caffeine. Keep in mind, however, that this also removes some flavor and aroma compounds.