Green tea is made from the same plant as the more common black tea you may be used to drinking. Unlike black tea, green tea leaves are not fermented, which may preserve more of their healthful antioxidants. Concentrated extracts of green tea leaves are often sold as supplements. Green tea extracts are used for weight loss and stomach problems, and to prevent cancer, but their effectiveness is unproven. Talk to your doctor before using green tea extracts.
Side Effects
Green tea extracts may be safe for short-term use, but they can cause side effects. Side effects include indigestion, constipation and allergic reaction. There are also a few rare reports of liver damage. If you have liver disease, do not take green tea extracts without consulting your doctor first, as they might worsen your condition.
Caffeine Effects
Some green tea extracts contain caffeine, which can pose some risks. Caffeine effects can include headache, nervousness, insomnia, vomiting, diarrhea, personality changes, irregular heartbeat, tremor, indigestion, lightheadedness, ringing in the ears, seizures, impaired iron absorption and confusion. Purchase an extract that says "caffeine-free" on the label. If you are pregnant or breastfeeding, check the label to be sure you are not consuming too much caffeine. Do not consume more than 200 mg of caffeine per day, from green tea extracts or other sources like coffee, because it has been linked to an increased risk of miscarriage. The caffeine in green tea extracts may also worsen anxiety disorders, stomach ulcers, glaucoma, anemia, bleeding problems, kidney disease, heart conditions, diabetes, osteoporosis and high blood pressure.
Drug Interactions
Consult your doctor or pharmacist before taking green tea extracts if you are already taking any prescription medications. Green tea extracts may impair the effectiveness of your medication or increase the risk of side effects. For example, green tea extracts may increase the risk of bleeding and should not be taken in combination with blood thinners or other drugs that increase bleeding risks. These include warfarin, heparin, aspirin and ibuprofen, and anti-platelet drugs like clopidogrel. Because green tea extract may affect the liver, do not take it in combination with any medications that also affect the liver. These include acetaminophen, cholesterol-lowering drugs like lovastatin, fluconazole, phenytoin, and antibiotics like erythromycin. In addition, the caffeine in some green tea extracts may interact with drugs such as amphetamines, ephedrine, antibiotics, birth control pills, hormone replacement therapy, cimetidine and lithium. Do not take green tea extracts if you are undergoing chemotherapy for cancer, as there is a risk it will interfere with your treatment.
Uses
Because of its caffeine content, green tea extracts are probably effective as a way to boost alertness. Green tea extract is also used in an FDA-approved treatment for genital warts. There is too little scientific evidence to know whether green tea extracts work for their most common uses. These include weight loss and reducing the risk of high blood pressure, stroke, diabetes, osteoporosis, breast cancer and prostate cancer. More research is needed.
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