It's been said that too much of anything is a bad thing. Apparently, this holds true with green tea as well. While it's been said that the polyphenols found in the drink can prevent heart diseases and cancer, large quantities of same substance can also cause kidney and liver damage.

Chung Yang of Rutgers from the State University of New Jersey has said that "people shouldn't be too alarmed by this, but those taking supplements may experience problems." He gave a ballpark figure of about 10 small cups of green tea as a good amount for individuals to consume. However, for those who are taking supplements, he warns that they may contain up to 50 times the polyphenol as one cup of green tea.

The credibility of this study is strengthened further by Yang's citations of experiments conducted on rodents and dogs which were given large quantities of polyphenols and died from liver poisoning. It has also been documented that some people who were overdosing on green-tea-supplements were diagnosed with liver toxicity. This was promptly cured by stopping the intake of the supplements, but is said to have resurfaced after regular consumption of the pills.