Green tea interactions and adverse reactions:
- Green tea has been quoted by multiple sources to contain a range of 120 to 160 mg of catechins per cup and an average of 23 mg of caffeine per cup (range of 11-48mg) but with high variability.
- Preventive Health Advisor recommends that liver function tests be obtained at the discretion of a primary care provider for green tea consumption of 5 cups per day or greater at baseline due to high a variability in green tea catechin content.
- Green tea extract is not recommended due to increased risk of hepatotoxicity with a higher concentration of catechins which it provides.
- While drinking green tea, patients should be advised to avoid drugs metabolized by the liver such as acetaminophen.
- According to Schönthal, the following adverse reactions have been reported (116):
- 34 case reports of hepatotoxicity, tremor, headache, pain, paresthesias, insomnia, palpitations, nausea, dysphagia, flatulence, and bloating.
- Green tea may reduce absorption of iron supplements, pseudoephedrine, theophylline, aminophylline, warfarin, codeine, atropine, ephedrine, carbinoxamine, dextromethorphan, Lomotil®, and Lonox.
- Green tea may increase the action of ephedrine, pseudoephedrine, theophylline, aminophylline, and reduce the effectiveness of adenosine, bortezomib, and sunitinib.
- Green tea contains caffeine which is generally recognized as safe by the FDA and AMA but can be dangerous with adverse effects such as high bp, stroke, and arrythmias reported. If more than 4 cups of caffeinated beverages are consumed per day, it is prudent to seek physician and/or pharmacist approval of caffeine consumption with any medications or supplements.
- When green tea is consumed in the form of whole leaves, or if it is steeped long enough to contain tannins, vitamin K is generally present in amounts significant enough to counteract the effects of warfarin (117,118), but if green tea is steeped for a short time, and the leaves are not consumed, green tea has very low concentrations of vitamin K (182).
- Caution use of whole green tea leaves or powder in patients taking warfarin which may make achievement of therapeutic PTINR difficult. Vitamin K levels in coffee and tea was performed which revealed that vitamin K concentrations were about 0.03 μg/100 mL or less, and according to this source, brewed tea or coffee contains extremely small amounts of vitamin K and is not a dietary source (119).
- Consumption of green tea at a dose of 4-6 cups daily for 6 months (480-960 mg of green tea catechins) has resulted in occasional episodes of toxic hepatitis, and the risk appeared to increase with chronic use (120). Caution use of green tea in patients with other forms of hepatitis, liver dysfunction, use of other medications cleared by the liver such as acetaminophen.
- No adverse effect of green tea was found in a 12-week RCT but the study was fairly short term and both the study group and the control group had a low incidence of elevated liver function tests (115).
References:
111.Kim A, Chiu A, Barone MK, Avino D, Wang F, Coleman CI, Phung OJ. Green tea catechins decrease total and low-density lipoprotein cholesterol: a systematic review and meta-analysis. J Am Diet Assoc. 2011 Nov;111(11):1720-9. http://www.ncbi.nlm.nih.gov/pubmed/22027055