Most teas brewed from green tea sold in stores in the U.S. provide about 10 to 40 mg per cup of the key green tea compound EGCG and 5 to 20 mg of caffeine. ConsumerLab.com's tests found that green tea supplements provided 22 mg to more than 300 mg of EGCG in a suggested daily serving and zero to 136 mg of caffeine per serving, depending on the product. Tests of bottled green teas found EGCG levels ranged from 4 to 47 mg per cup, and caffeine ranged from 8 to 37 mg. Preliminary studies suggest that EGCG and related catechin compounds in green tea may aid in weight management and reduce the risk of certain types of cancer.
"Although a label says 'green tea,' the actual amounts of EGCG and caffeine you get from a supplement or drink vary widely by brand," said Tod Cooperman, MD, president of ConsumerLab.com. "Labels often don't tell you what you're getting and some are plain wrong.”
One "GMP certified" green tea supplement tested by ConsumerLab.com contained only 38% of the claimed EGCG. It also contained an unusually high amount of caffeine—136 mg per capsule, which is 40 mg more than a cup of brewed coffee and several times as much as most other products—although there is no mention of caffeine on the label. One bottled green tea contained only 63% of the listed amount of green tea catechins listed on its label.
Across the products, ConsumerLab.com found the cost to obtain 200 mg of EGCG to range from 10 cents to over $70.