Does Green Tea Extract Interact With Medicines?

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A staple drink of many Asian nations for thousands of years, green tea has a rich store of many beneficial nutrients, including catechins, a group of potent antioxidants. The use of green tea extract has been suggested to ward off a host of conditions ranging from heart disease to obesity. According to the University of Pittsburgh Medical Center, research on some fronts seems promising but has produced mixed results. Whether or not using green tea in supplement form will produce any therapeutic benefit has not been conclusively established. Like drugs, natural supplements can sometimes produce negative effects, and some potential medication interactions have been noted with the use of this supplement. Check with your doctor before using green tea extract or any herbal treatment if you take prescription drugs.

Sedatives and Antidepressants

The caffeine content of green tea extract could interfere with the actions of benzodiazepines, a class of medication commonly used to treat anxiety and related disorders. This means potentially reduced effectiveness in quelling anxiety, nervousness, insomnia and related symptoms. Simultaneous use of green tea and MAOI’s – a commonly prescribed class of antidepressants -- could cause dangerous increases in blood pressure, according to the University of Maryland Medical Center. It might also decrease the effectiveness of lithium, used to treat bipolar disorder.

Blood-Thinning Drugs, a site that compiles information from various medical databases, reports that the vitamin K content of green tea could potentially negate the effects of blood-thinning medications like warfarin, as this vitamin promotes blood clotting.

Cancer Therapies

Some debate exists over the use of antioxidant supplements while undergoing chemotherapy, as in some instances they could make the drugs less effective in destroying malignant cells. The University of Maryland Medical Center reports research that found that using green tea made certain chemotherapy drugs actually work better, but in one instance, it triggered the growth of a certain gene that made prostate cancer cells less sensitive to the actions of chemotherapy drugs. Because of the potential to interfere with the effectiveness of these treatments, check with your doctor about the appropriateness of using green tea if you are currently undergoing chemotherapy. You might not need to avoid green tea completely, but rather time your intake of the supplement based on your treatment schedule. Only your doctor can safely make this determination. The Memorial Sloan Kettering Cancer Center reports green tea might also negatively interact with tamoxifen, a widely used breast cancer drug.

Other Interactions

Other drugs specifically noted to interact with green tea include adenosine, atropine, iron and folic acid medications, irenotecan, verapamil, clozapine, ephedrine, birth control pills and phenylpropanolamine.

Your liver produces various enzymes that process the drugs you consume. The Sloan Cancer Center notes green tea was found to interfere with the actions of P450 3A4; if you take any drugs metabolized by this enzyme, use of green tea could potentially trigger negative effects like increased levels of the drug building up, which can lead to issues like toxicity and increased risk of side effects associated with these treatments.