Green tea is often the refuge of heart disease patients, who are told it is a much healthier source of caffeine than tea and coffee.
However, Japanese researchers have discovered it may block the effects of nadolol, a commonly prescribed pill to reduce high blood pressure.
They tested people who drank green tea as well as taking the beta-blockers, and found that they had lower circulating blood levels of the drug, the BBC reported.
The Mail Online added: "Drinking green tea cut the amount of drug that made its way into the bloodstream by three-quarters. It also meant that the drug, which is also taken to treat angina and irregular heartbeats and to prevent migraines, was less effective at lowering blood pressure.
"It is thought that plant chemicals in green tea stop nadolol from being ferried from the gut into the bloodstream, where it can get to work on reducing blood pressure."
The study was published in the Clinical Pharmacology & Therapeutics journal.
At present, the leaflet accompanying use of the tablets say that certain herbal remedies can interfere, but it doesn't include green tea.
The BBC added: "Sotiris Antoniou, Royal Pharmaceutical Society spokesman and a consultant pharmacist in cardiovascular medicine, suggested to blood pressure patients who still want to drink green tea that leaving a four-hour gap between cups and taking their medicines might get round the problem.
"He said: 'This has yet to be confirmed and is only extrapolated from our experience with grapefruit for this type of interaction.'"
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How To Lower Your Blood Pressure
According to the <a href="http://www.who.int/en/" target="_hplink">World Health Organisation</a> (WHO) the eight key risk factors (alcohol use, tobacco use, high blood pressure, high body mass index, high choles terol, high blood glucose, low fruit and vegetable intake, and physical inactivity) account for 61% of all cardiovascular deaths and over three quarters of all coronary heart disease. "Changing your diet and lifestyle can help to achieve a significant drop in your blood pressure levels, whether or not you are taking tablets," says Linda Main, Dietician for <a href="http://www.heartuk.org.uk/" target="_hplink"><strong>HEART UK</strong></a>. Take a look at the simple lifestyle changes you can make today to help lower blood pressure and maintain a healthy heart.
Drink alcohol in moderation. No more than 3 to 4 daily units a day for men and no more than 2 to 3 units for women.
Follow the Dietary Approaches to Stop Hypertension (DASH) eating plan. Based on research findings which show that a diet low in saturated fat and salt, but high in fruit and vegetables, wholegrain foods and low fat dairy foods, can significantly lower blood pressure within two weeks. It is rich in nutrients such as potassium, calcium, magnesium and fibre.
Meditation can help maintain a calm and focused mind, but one side benefit of that relaxation could also help with blood pressure. When relaxed, the body produces more nitric oxide, <a href="http://www.npr.org/2008/08/21/93796200/to-lower-blood-pressure-open-up-and-say-om">which in turn helps blood vessels to open up, reducing the pressure of the blood flowing through</a>.
Adopt A Pet
Research shows that <a href="http://www.webmd.com/hypertension-high-blood-pressure/guide/5-ways-pets-improve-your-health">pet owners have lower blood pressure</a> (also: lower cholesterol and heart disease risk), thanks to the anxiety-reducing qualities of an animal companion.
Work On Your Marriage
In one 2008 study in the Annals of Behavioral Medicine, <a href="http://www.cbsnews.com/2100-500368_162-3955956.html">researchers found that happily married adults had better blood pressure</a> than happily single and unhappily married adults.
This one's a no-brainer, but exercise is one of the best ways to lower blood pressure. There are many ways that the simple act of moderate exercise can improve your blood pressure (and overall health). First, it helps with other risk factors for hypertension, like extra weight and stress. But exercise also improves the strength of your heart so that <a href="http://www.mayoclinic.com/health/high-blood-pressure/HI00024">it can more effectively and efficiently pump blood, which lowers the pressure on the arteries</a>.
Stick To One Or Two Drinks
Moderate drinking -- one drink for women and men over 65 and two drinks for younger men -- can actually help reduce blood pressure. <a href="http://www.mayoclinic.com/health/high-blood-pressure/HI00027">But more than that has the opposite effect</a>, according to the Mayo Clinic.
Monitor Your Caffeine
There is some evidence that caffeine can temporarily increase blood pressure, though it's unclear if there is a long-term effect. The <a href="http://www.mayoclinic.com/health/high-blood-pressure/HI00027/NSECTIONGROUP=2">Mayo Clinic recommends</a> checking blood pressure 30 minutes after a cup of coffee or caffeinated soda to see if the effect remains.
Quit Smoking -- And Smokers
Of course, for this and many other reasons, you should quit smoking. But even second-hand smoke can have a damaging effect on your blood pressure <a href="http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/UnderstandYourRiskforHighBloodPressure/Understand-Your-Risk-for-High-Blood-Pressure_UCM_002052_Article.jsp">because it damages arteries</a>.
Choose Pressure-Lowering Foods
Several foods have been found to naturally lower blood pressure. Things like chili peppers, chocolate, beans and bananas have all been proven to lower blood pressure in humans or in trials with rats. <a href="http://www.huffingtonpost.com/2012/03/28/raisins-and-7-other-foods-lower-blood-pressure_n_1382535.html#slide=817449">Read on for more here</a>.
Keep Weight Under Control
Eating well is essential to maintaining healthy blood pressure, but even if you live on <a href="http://www.huffingtonpost.com/2012/03/28/raisins-and-7-other-foods-lower-blood-pressure_n_1382535.html#slide=817449">beans and bananas</a>, extra pounds could harm you. In fact, one Italian study found that <a href="http://www.sciencedaily.com/releases/2007/09/070928180348.htm">hypertension in overweight patients was a secondary condition, caused by the excess weight</a>. In other words, once the weight was lost, the high blood pressure went with it.
Stay Away From Salt
Perhaps the best known advice for healthy blood pressure is maintaining a low sodium diet. Follow the <a href="http://health.gov/dietaryguidelines/faq.asp">USDA's Dietary Guidelines for Americans</a>: a max of 2,300 mg of sodium for healthy, young adults -- or 1,500 mg a day or fewer for those who are over 50, African-American or suffering from diabetes or chronic kidney disease.
So why is it recommended in the first place? Green tea is less processed than other tea, so it has a high level of antioxidants, which is good for the immune system.
However, simply because green tea may interact with blood pressure tablets such as nadolol doesn't mean it isn't a healthy addition to a person's diet. It has also been praised for having anti-cancer properties due to its antioxidant levels.
And - for older people - it can play a very beneficial role in bone strength.
"Osteoporosis is a major public health concern but new research suggests that polyphenols in green tea may help improve bone quality and strength through many proposed mechanisms," said a report in the American Journal of Clinical nutrition.
"In fact, one study found that tea drinking was associated with a 30% reduced risk in hip fractures among men and women over 50 years old. In a study of 150 postmenopausal women, researchers reported that 500 mg green tea extract (equivalent to 4-6 cups of green tea daily), alone or in combination with Tai Chi, improved markers for bone formation, reduced markers of inflammation and increased muscle strength in study participants. Numerous other studies have found that green tea flavanols provide a restorative effect to bone remodeling to help maintain bone density and slow bone loss."
If you are concerned about any of the above, talk to your GP.