Green tea is generally prized as a healthy beverage, due to its high levels of antioxidants. However, a recent study by Fukushima Medical University in Japan has shown that it can actually inhibit uptake of drugs commonly used to treat high blood pressure.
The beta blocker Nadolol (which is distributed under the brand name Corgard) is used to block adrenaline and cause the heart to beat more slowly and gently. It is used in high blood pressure patients and those at risk of heart attacks, and is also used to treat some other conditions such as anxiety. When a study group of ten subjects were asked to take Nadolol after either water or green tea, it was found that the consumption of green tea caused a reduction of Nadolol in the patients’ blood plasma of up to 75% – seriously inhibiting the effectiveness of the drug. It is thought that this happens because the tea blocks a drug transporter found in the gut that is needed to mobilise Nadolol.
This small scale study did not look into whether other types of tea cause a similar effect, or whether other beta blockers are affected by green tea. Patients using Nadolol are advised to avoid green tea while taking the drug, and those who wish to keep drinking it are urged to consume it only four or more