We’ve all gotten used to thinking of green tea as a veritable fount of good health because it’s a great source of antioxidants that reduce cholesterol, triglycerides and the risk for cancer, cardiovascular disease and Parkinson’s disease. But: For certain people, green tea actually may do more harm than good—by interfering with a type of blood pressure medication called a beta-blocker. Here’s the news from a recent study…
For two weeks, one group of participants drank 24 ounces of green tea every day…a second group avoided green tea and drank water instead. After the two weeks were up, all participants were given a single 30-mg dose of the beta-blocker nadolol (sold in the US as Corgard and also used in the combination drug Corzide). Then, numerous times over the next 48 hours, blood and urine samples were collected from the participants so that researchers could measure the amount of the drug that was circulating in the blood and the amount excreted in urine. Participants’ blood pressure and pulse rates also were measured.
After a two-week break, the process was repeated but with the participants switching beverages—so that the former green-tea-drinking group stuck to water, and the former water group drank the three cups of green tea each day for two weeks. Then, as before, everyone took a dose of the beta-blocker drug and gave blood and urine samples. Results…
Explanation: Based on laboratory experiments, the researchers suspect that a compound in green tea, epigallocatechin-3-gallate (EGCG), inhibits the ability of specialized transporter cells to move the blood pressure drug across the intestinal wall and into the bloodstream. Ironically, EGCG is the same antioxidant compound credited with giving green tea many of its health-boosting effects.
What we still don’t know: This was a small study, and many questions remain. For instance, does green tea interfere with the absorption of all types of beta-blockers or just nadolol? Do black tea, oolong tea and white tea also reduce the effects of blood pressure medication, or is the problem limited to green tea? Would it be OK to drink, say, just one cup of green tea daily…or would even that small amount still block the absorption of the blood pressure drug? Might green tea extract, a popular supplement, also interfere with beta-blocker medication in the same way that the beverage does? (The amount of green tea consumed per day in this study provided 322 mg of EGCG, which is less than the amount of EGCG found in many green-tea-extract supplements, especially those marketed as fat burners.) Clearly, more research is needed.
What to do in the meantime: If you’re taking nadolol or another beta-blocker and you’re accustomed to drinking green tea, discuss these study findings with a nutrition-oriented doctor. If your blood pressure is well-controlled, your doctor may say it’s OK to carry on as you are. However, if your blood pressure is not well-controlled, you may be advised to reduce or cut out green tea to see whether this helps control your blood pressure better. Either way, of course, it’s best to follow a healthful diet that helps keep blood pressure down—so check out “More on How Foods Affect Blood Pressure,” above.