Green tea and green tea supplements have become very popular in the last few years and have been touted as a panacea for many illnesses. While drinking green tea may be beneficial, there is less evidence to support the use of green tea extract, which is often marketed and used for weight loss. While there is some evidence to support this, there may be some risk. In a Clinical Observation published in The Annals of Internal Medicine (2006; 144: 68-69), Dr. Herbert Bonkovsky reports on a case of liver toxicity related to green tea extract.
The patient, a 37 year old woman, had arrived at the hospital complaining of abdominal pain, nausea and jaundice. Testing for infection was negative, but a liver biopsy showed liver damage. She had been taking "The Right Approach Complex", a weight loss supplement containing green tea extract. When she stopped taking the supplement, her liver tests returned to normal.
One year later the same patient was admitted to the hospital again with the same symptoms. A month earlier she had started taking the same supplement. Testing of her liver showed similar results to the previous year and again returned to normal after stopping the supplement for the second time. This is what doctors call a "positive rechallenge," meaning that the supplement caused problems with a second use or "challenge." This is generally taken as evidence of a medication or supplement as the cause of a side effect.
While one popular website still reports, "To date, the only negative side effect reported from drinking green tea is insomnia due to the fact that it contains caffeine," this is clearly not the case with supplements. Dr. Bonkovsky reports eight other cases where use of green tea extract caused liver problems.