In 1999 a weight loss product was commercialised in France that was based on an ethanolic extract of green tea (Camellia sinensis). Since then, numerous cases have been described in literature associating this product with elevated liver enzymes (a marker of liver damage) with at least one known liver transplant case. The evidence implicating this proprietary product in liver damage is strong.
The curious fact is that green tea has been consumed in vast quantities by millions of people as a beverage for more than 50 centuries with no previous implication in liver damage. In fact, many health benefits have been attributed to the regular consumption of green tea. So what has happened that has made green tea potentially dangerous to health?
Look at the way green tea is traditionally prepared. When consumed as a beverage it is extracted with hot water. For weight loss products the green tea was extracted with a high percentage of alcohol. There could be some factor in green tea extracted by the ethanol that triggers the reaction in susceptible individuals, or perhaps some protective factor is lost when alcohol is used as the extraction solvent.
On the basis of this evidence, green tea should only be used as a dried aqueous (hot water) extract in a beverage, tablet or capsulated product, thereby matching traditional use. If you take a capsule or tablet with green tea as an ingredient, consult your herbalist to ensure it was extracted using hot water.
Oh, and 2-4 cups of green tea a day is proving to have positive health benefits. Cheers!