Consuming green tea (Camellia sinensis) extract or its associated catechins is not expected to have a clinically significant impact on major CYP450 or uridine 5’diphospho-glucuronosyltransferase enzyme substrates or P-glycoprotein (P-gp) substrates, study authors concluded in a review published in Planta Medica.  

Authors Ahmed A. Albassam, from Prince Sattam Bin Abdulaziz University, Saudi Arabia, and John S. Markowitz, from University of Florida College of Pharmacy, reviewed available in vitro, animal, and clinical studies assessing the effects of green tea extract and associated catechins on drug-metabolizing enzymes and drug transporters. 

Findings from in vitro studies suggested that green tea extract and (−)-epigallocatechin-3-gallate, its main catechin, inhibited the activity of CYP1A1, CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2D6, and CYP3A4; UGT1A1 and UGT1A4 isoforms were also inhibited by the catechin.  

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Findings from animal studies suggested that green tea extract and/or (−)-epigallocatechin-3-gallate significantly increased the bioavailability of diltiazem, verapamil, tamoxifen, simvastatin, 5-fluorouracil, and nicardipine. The bioavailability was decreased for quetiapine, sunitinib,clozapine, and nadolol. Green tea extract and (−)-epigallocatechin-3-gallate were not found to inhibit any major CYP450 enzymes. 

Drug transporters such as P-gp, OATP1A1, OATP1B1, OATP1B3, OATP2B1, OCT1, OCT2, multidrug and toxin extrusion 1, and multidrug and toxin extrusion 2-K were potentially inhibited by green tea extract according to in vitro studies.

One clinical study indicated that OATP1A1 was inhibited by (−)-epigallocatechin-3-gallate whereas P-gp was not affected. 

It was generally concluded that ingestion of green tea extract or its associated catechins is not expected to result in clinically significant influences in the evaluated substrates. “However, some caution is advised in the consumption of significant amounts of green tea beverages or green tea extract in patients prescribed known substrates of organic anion transporting polypeptide, particularly those with a narrow therapeutic index,” noted study authors.

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