The study, published in Clinical Pharmacology & Therapeutics, investigated the effects of green tea on pharmacokinetics and pharmacodynamics of the beta-blocker nadolol in healthy people - finding that nadolol's prescribed effect of lowering blood pressure was blunted in those who drank green tea.
The Japanese researchers behind the study found that the beverage blocks special cell transporters which normally help the body absorb nadolol - meaning that people who drank the green tea alongside taking their tablets ended up with lower circulating blood levels of the drug.
Researchers gave ten healthy volunteers a single oral dose of 30 mg nadolol with green tea or water after repeated consumption of green tea (700 mL/day) or water for 14 days, before measuring the pharmacokinetics and pharmacodynamics of the drug.
Green tea was found to "markedly" decrease the effects of nanolol on systolic blood pressure, with further tests in the laboratory showing that green tea significantly inhibited OATP1A2-mediated nadolol uptake.
"These results suggest that green tea reduces plasma concentrations of nadolol possibly in part by inhibition of OATP1A2-mediated uptake of nadolol in the intestine," said the team behind the study.
Source: Clinical Pharmacology & Therapeutics
Published online ahead of print, doi:10.1038/clpt.2013.241
"Green tea ingestion greatly reduces plasma concentrations of nadolol in healthy subjects"
Authors: S Misaka, J Yatabe, F Müller, et al