Is your diet affecting your medicines?

Lesley Dobson / 11 July 2016

If you’re taking medicines for the long term, and/or other drugs for occasional health issues, remember to watch what you eat and drink.

Whether you’re on a long-term course of medication – for high blood pressure for instance – or on a short course of drugs for a health hiccup, it’s important to watch what you eat and drink.

This is important for your health because some foods can affect the drugs you take. Known as food-drug interactions, this can mean that the drugs may not work as well as they should. On the other hand they may become more concentrated in your body, and can even become so toxic that they may put your life at risk.

Understanding drug interactions

 As we grow older our bodies can react in different ways to the medicines we take. So as we age our liver and kidneys may slow down, and take longer to process the drugs we take. It’s a good reason to pay extra attention when taking medicines.

Some drugs are well known for reacting with other drugs and certain foods and alcohol.

Foods you shouldn't eat if you're on Warfarin

Warfarin is one of these. Warfarin is an anticoagulant medicine. This means that it makes it harder for your blood to clot. Warfarin is often prescribed for people who have had health problems because of blood clots in the past.

Typical examples include having had a heart attack, a stroke, or a blood clot in the lungs (a pulmonary embolism).  People who have atrial fibrillation (irregular heart rhythm that can cause blood clots in the heart) or an increased risk of blood clots after an operation may also be prescribed warfarin.

Visit our guide to cardiovascular disease for more information on a range of conditions

Warfarin can react with other medicines, for instance, aspirin and ibuprofen, and some herbal supplements. It can react with certain foods too, especially those containing vitamin K – these include spinach, broccoli and other green leafy vegetables, and some vegetable oils. If you are taking warfarin, ask your doctor which foods you should avoid.

The pros and cons of vitamin K-rich kale

Give up grapefruit if you're on one of these drugs

Grapefruit and grapefruit juice are known to cause potentially dangerous interactions with a number of drugs. This is because certain chemicals in grapefruit interfere with the breaking-down of some drugs. The result can be that we end up with too much of these drugs in our bodies, with potentially harmful effects.

There are quite a large number of drugs that interact with grapefruit. These include drugs that treat cancer, high cholesterol, heart and blood vessel problems, nausea, urinary tract infections and central nervous system problems.

Always check with your doctor – GP or specialist – on whether it’s safe for you to have grapefruit and grapefruit juice while taking any drugs. If you aren’t sure, it’s best to avoid grapefruit until you’ve asked your doctor for advice.

Take care with milk

Other foods that can interact with drugs include milk, which can reduce the amount of some antibiotics your body absorbs, if you take them together. Leave a couple of hours between taking your medicines and having milk or cheese.

You should cross cheese, wine and beer off your shopping list if you are taking monoamine oxidase inhibitors (MAOIs) antidepressants. The combination of any of these every-day food and drink items with these antidepressants could cause a sudden rise in your blood pressure. This rise in your blood pressure could put you at risk of having a stroke.

Stay safe when taking medicines

  • When your doctor prescribes drugs that react with certain foods and drinks they should explain the risks of taking these foods and drinks with these medicines.
  • If you forget which drugs react with certain foods, check on the information leaflet that comes with your medicines.
  • If you are worried that you might have eaten or drunk something that might have reacted with any of the drugs you are taking, phone your local pharmacy or your GP to check.
  • Worried you’ll forget what you can and can’t eat? Write a list of the food and drink that you need to avoid when taking your medication, and a list of the medication you take. Put this list in a place where that you can easily find it – on your fridge door for instance. 
The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.