Can Green Tea Adversely React With Any Prescription Medications?

The potential health benefits of green tea, its extracts and its active constituents are the subjects of active scientific research. Although the evidence supporting many of these benefits is inconclusive, green tea is touted as a treatment or preventive for heart disease, obesity, cancer and viral infections. With all the good news, you may be wondering if you should consume more green tea, but it's always prudent to ensure it won't interact with any medications you may be taking.

Active Ingredients

Green tea contains a variety of polyphenol antioxidants, the most important of which are the catechins. In fact, green tea is 20 to 45 percent polyphenols by weight, and, depending on growing conditions, up to 80 percent of these are catechins. Among the catechins, epigallocatechin gallate, or EGCG, is the most prevalent in green tea, and has been the most extensively studied. Green tea also contains caffeine, tannins and other compounds that could conceivably interact with medications.

Folic Acid

EGCG has been shown to inhibit dihydrofolate reductase, an enzyme that is needed for the synthesis of DNA. Dihydrofolate reductase is involved in the transformation of folic acid, a B vitamin, into its active form within your cells. While one study in "Cancer Research" suggested this property may help explain some of green tea's anticancer effects, the authors of a review in "American Family Physician" raised the issue of a potential increase in birth defects among infants born to folate-deficient mothers who drink green tea.

Anticoagulants

Depending on its source and preparation, green tea contains variable amounts of vitamin K. If you consume large amounts of green tea, you could also be getting a healthy dose of vitamin K, which interferes with the activity of a widely prescribed anticoagulant called warfarin, or Coumadin. A 1999 report in "The Annals of Pharmacotherapy" describes the case of a man with an artificial heart valve whose clotting time dangerously decreased when he started drinking a half-gallon of green tea daily. Since green tea inhibits platelet activity, it can also enhance the activity of aspirin and other anti-platelet drugs.

Caffeine and Tannin Interactions

If you are taking a sedative, such as diazepam, alprazolam or lorazepam, the caffeine in green tea could make your medication less effective. According to the University of Maryland Medical Center, people who take beta-blockers for high blood pressure or heart rhythm abnormalities should probably avoid green tea, because caffeine can aggravate their underlying condition. Green tea can cause severe increases in blood pressure when taken with monoamine oxidase inhibitors, or MAOIs, such as phenelzine. It may also reduce the effectiveness of other psychoactive medications, such as lithium or clozapine. According to "Physicians' Desk Reference for Herbal Medications," the tannins in green tea could interfere with the absorption of certain minerals, such as iron, or alkaline medications, such as theophylline.

Recommendations

Green tea is well-tolerated by most people and, with some notable exceptions, drug interactions are unlikely. Scientists have not decided how much green tea is needed to confer optimal health benefits, nor is there a clear definition of what constitutes "excessive" consumption. If you are pregnant or taking a medication or a mineral supplement, ask your physician if green tea is advisable for you.