Japanese scientists have found that drinking green tea may lessen the efficacy of the high blood pressure drugs such as nadolol, according to media news Wednesday. Researchers found that people who drank green tea while taking nadolol had lower circulating blood levels as compound was found in the tea that prevents the medication from taking effect. Sotiris Antoniou, an expert in cardiovascular medicine, advised high blood pressure patients who still want to drink green tea to wait four to five hours after taking high blood pressure drugs.