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Heart medicines and your diet - interactions to watch

What do grapefruit juice, cranberry juice, potassium and vitamin K have in common? You might not know it, but these are just some of the things you need to be wary of if you’re taking particular medicines for your heart health.

Although some combinations sound unlikely, it’s important to get in the know because certain food and drug interactions can:

  • stop your medicine from working properly
  • cause a side-effect from your medicine
  • increase the effects of your medicine
  • change the way your body processes or uses a food

To help you get to grips with some of these interactions, we’ve looked at four main ones to consider if you take medicines for your heart.

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  • Grapefruit juice Grapefruit juice

    For many of us, drinking a glass of grapefruit juice in the morning is a great way to start the day. But if you’re taking statins, you may need to avoid grapefruit juice, or limit how much you have.


    Statins are medicines that lower the amount of bad (LDL) cholesterol in your blood. This in turn helps to reduce your risk of cardiovascular disease, including heart attack and stroke.

    Grapefruit juice can interact with certain types of statins (particularly simvastatin and atorvastatin), causing side-effects. The juice blocks an enzyme in your liver that helps process the medicine. This causes a higher concentration of the medicine to enter your bloodstream. This can cause damage to your liver, muscles and kidneys.

    If you take statins, try not to drink any grapefruit juice or limit the amount you have. However, some statins (for example, pravastatin) don’t interact with grapefruit juice. So if you’re a big fan, it may be worth asking your doctor for an alternative.

  • Cranberry juice and vitamin K Cranberry juice and vitamin K

    The juice of this sweet, red berry may seem harmless, but if you’re taking the anticoagulant (blood thinning) medicine, warfarin, it’s a no go. Foods high in vitamin K may also need to come off your shopping list.


    Anticoagulant medicines work by thinning your blood. They help to stop blood clots forming in your veins and the chambers in your heart. You may be offered an anticoagulant such as warfarin if you have atrial fibrillation. This condition increases your risk of stroke, so this medicine can help stop a clot forming and help reduce the risk.

    Cranberry juice can interact with warfarin and increase your risk of bleeding. Experts don’t know how much cranberry juice is dangerous or if other cranberry products, such as capsules, are harmful too. Therefore, the advice is to steer clear of cranberry juice and related products if you’re taking warfarin.

    Cranberry juice is only recommended if your doctor agrees that the benefits of having it outweigh any risks. Talk to your doctor about any concerns or questions you have.

    Large amounts of vitamin K-rich foods can lessen how effective warfarin is. These include beetroot; green, leafy vegetables (such as spinach, Brussels sprouts and lettuce); green tea; mango; avocado and even ice cream. Talk to your doctor about your diet and how you should modify it to allow your medicine to work effectively.

  • Potassium Potassium

    For many of us, cutting down on salt is a good thing. This may mean that you’re choosing salt substitutes instead of salt. However, if you’re taking angiotensin converting enzyme (ACE) inhibitors or angiotensin ll antagonists, be wary of salt substitutes. This is because they contain potassium.


    ACE inhibitors are used to treat several conditions including heart failure and high blood pressure. They work by stopping an enzyme called angiotensin I from converting into angiotensin II. It’s important to stop this conversion because angiotensin II narrows your blood vessels, which causes your blood pressure to rise. These medicines allow your blood vessels to dilate, improving the blood flow to your heart.

    ACE inhibitors can increase the amount of potassium in your body. Some foods or supplements that are high in potassium may increase the amount in your body further. Too much potassium can be harmful, causing nausea, stomach pain and diarrhoea, or even problems with your heart.

    If you’re taking any supplements that contain potassium or salt substitutes, you should stop taking them before you start taking ACE inhibitors.

    Bananas, oranges and green, leafy vegetables are all high in potassium. Some experts advise that you may need to be careful about how much you eat when taking these medicines. It doesn’t mean you can’t eat these foods at all; they’re an important part of a balanced diet. Large amounts, however, could possibly have an unwanted effect so speak to your doctor about any questions you have.

  • Worried about your heart health?

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  • Understand your medicine Understand your medicine

    Whenever you’re taking any medicine, it’s vital that you understand what you’re taking, how to take it and are aware of any interactions or side-effects.

    • Read the patient information leaflet that comes with your medicine. This is important as you may find that the medicine you’re taking has a list of foods and drinks you shouldn’t have.
    • Do your research. Look for reputable sources of information that will help you understand why your medicine interacts with certain products.
    •  Ask your doctoror a dietitian questions about your treatment or medicine. If you’re in doubt, or have any questions, speaking up is always the best thing to do so you can be reassured.
  • Resources Resources

    Further information


    • Avoid food-drug interactions. National Consumers League and US Food and Drug Administration., accessed 9 January 2014
    • Joint National Formulary. British National Formulary (online). BMJ Group and Pharmaceutical Press., accessed 9 January 2014 (online version)
    • Lipid modification – CVD prevention. NICE Clinical Knowledge Summaries., published December 2008
    • Current problems in pharmacovigilance. Committee of Safety of Medicines, Medicines and Healthcare Products Regulatory Agency (MHRA), October 2004.
    • Atrial fibrillation. National Institute for Health and Care Excellence (NICE), 2006.
    • Drug-nutrient interactions and prescription of nutritional products. Oxford handbook of nutrition and dietetics (online). Oxford Medicine Online., published January 2012 (online)
    • ACE inhibitors. British Heart Foundation., accessed 14 January 2014
    • Potassium. Food Standards Agency., accessed 14 January 2014
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