Drinking green tea may not be a good idea if you're taking drugs to lower your blood pressure. A new study published in the journal Clinical Pharmacology & Therapeutics Jan. 13 found that drinking tea may actually lessen the efficacy of the drug nadolol commonly prescribed for treating high blood pressure.

For the study, the researchers recruited ten adults and gave them a single dose of 30 milligrams of nadolol (Corgard) after either three cups of green tea or water everyday for two weeks. When the volunteers' blood was tested, the researchers found that the concentration of nadolol was 76 percent lower in the group that drank green tea compared to the water-drinking group. They also discovered that the amount of nadolol detected in the urine was about 80 percent lower among those who drank green tea regularly.

The results were interpreted as a sign that green tea prevents nadolol from being absorbed well by the body. Follow up lab tests showed that green tea blocks a drug transporter found in the lining of the human gut that helps transport nadolol from the gut into the cells, where it can work on reducing blood pressure.

The researchers acknowledged that further studies are still needed to understand how green tea may react with drugs like nadolol but they have advised patients taking nadolol to avoid drinking green tea.

"Individuals who take nadolol and also consume green tea should be aware of this potential interaction and discuss this with their physician," said Dr. Gregg Fonarow, a professor of cardiology at the University of California in Los Angeles and spokesman for the American Heart Association.

Sotiris Antoniou, spokesman for the Royal Pharmaceutical Society and consultant pharmacist in cardiovascular medicine suggested a get around to this. He advised high blood pressure patients who still want to drink green tea to leave a four-hour gap between cups and taking their medicines.

"This has yet to be confirmed and is only extrapolated from our experience with grapefruit for this type of interaction," he said. "What is clear as healthcare providers is that we need to ask patients about their consumption of various fruits and supplements such as grapefruit and green tea, and this needs to be documented in the clinical notes, and where appropriate provide information on avoiding green tea or grapefruit, or better where possible to prescribe an alternative drug that is not affected by the consumption of green tea."

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