Foods that react with medications

Posted by:

Derby Chiropractors Ian Reed and Richard Nelson of WellBeing Clinics want to make you aware that a number of prescriptive and over the counter drugs can react with a wide variety of commonly eaten and healthy foods. This can result in the potentially dangerous reduction or an enhancement of a drugs activity in the body with its resultant knock on effects on your body systems. The humble grapefruit is probably one of the most well-known foods to react but there are others.  Recent study results have shown an even wider list of medications that grapefruit and some other citrus fruits, notably limes and Seville oranges (as used in marmalade) –have an effect on. Medical professionals have been aware for some time that these fruits alter the way our bodies take up certain drugs but the objective of the latest study was to pool research and draw up a more complete list.   There is actually quite a wide range and most of them are pretty common so it will pay us all to be aware of what they are and which drugs they affect.

The latest research on food Vs medication interactions

In this latest study researchers reviewed published studies of grapefruit/drug interactions to see how many drugs were affected.   The research is a review of all the known studies that have been published on grapefruit/drug interactions and included 102 randomised controlled trials, which is the best type of study for finding out if one thing, causes another.  Although the research is reliable, we still don’t know how common this problem is.

What types of drugs are affected by Citrus fruits?

The citrus fruits in are known to interfere with a wide range of drugs, including

  • Blood pressure drugs
  • Cholesterol lowering drugs
  • Antidepressants
  • Antihistamines
  • Antiretrovirals
  • Cancer drugs

For example, 200-250ml of grapefruit juice (a large pub wine glass) can increase the strength of a blood pressure-lowering drug called ‘felodipine’ by 3 times! Click  the table on the picture  to see which type of medications have the most serious interactions with grapefruit [lightbox style=”modern” image_path=”” popup=”” link_to_page=”” target=”” description=”Medical drugs affected by grapefruit” size=”portrait_thumb”]

Some of the more common food and  prescription medication interactions

[lightbox style=”modern” image_path=”” popup=”” link_to_page=”” target=”” description=”Foods that can react with medical drugs”  size=”two_col_large”]

Do all food/drug interactions work in the same way?

The simple answer is no.  We are all probably aware that we’ve been told certain drugs should not be taken with food, whilst other drugs must be taken with food to prevent stomach irritation. Foods can affect drug action in many ways.  The most common is when foods interfere with absorption, which can make a drug less effective. For example, calcium in milk can bind to the Quinolone antibiotics such as tetracycline, interfering with its absorption.  Nutrients or other components of food can also interfere with a drug’s metabolism, or how it is broken down in the body,  and then of course on the final leg of its journey through our bodies, foods can affect the elimination of drugs from our systems. The drugs often enter the body via a particular enzyme in the digestive system called CYP3A4.  It’s not a very catchy name but it is a vital part of your digestive process and has been harnessed to carry certain medications into your body and enable them to work properly.It seems that the citrus fruits in question contain substances called Furanocoumarins that interfere with CYP3A4 and the way in works and in so doing, stop some drugs from getting into the body and being able to work. Conversely, some drugs interfere with the absorption of nutrients.  For example, some cholesterol-lowering medications reduce the absorption of fat-soluble vitamins.  Others drugs affect the body’s use or elimination of nutrients, like diuretics, which can cause a depletion of potassium, and lead to a deficiency which can be extremely dangerous and even potentially fatal. Drugs against male impotence, including Viagra at, are able to reduce the risk of heart disease. The corresponding study was conducted by the specialists from the center of cardiac surgery. It was found that pills against erectile dysfunction can reduce arrhythmia (irregular heart rate), which often the causes death of the patients with heart failure. Besides, scientists followed a group of six thousand diabetics taking such drugs as Viagra.


This is the term given used to describe how much of a drug actually reaches the target tissue.  Of course it’s never simple is it?   We are all different and we all respond slightly differently to each medication.   So when it comes to interactions the same applies – one person could be very severely affected while another may perceive no symptoms at all. We are all very different and scientists are finding it very difficult to draw up a definitive list of food/drug interactions because of this.  Our individuality is further complicated by the fact that some of the foods identified as potential problems would have to be consumed in abnormally large quantities to be a real issue.

What could happen if I am affected?

It appears that the number of drugs that have a dangerous interaction with grapefruit has more than doubled in the past 4-years, from 17 in 2008 to 43 in 2012 (it is up to 85 in Canada though not all of these are available in the UK).  This is because the CYP3A4 enzyme is particularly effective method of delivery in many cases.

How can I be sure the symptom I am feeling is a side effect?

The best advice is, if you take prescription drugs, check the leaflet in the packet, ask your doctor or pharmacist to see if they are aware of any known food/drug interactions and if you are still worried, read up on it yourself.  The internet is jammed with information which of course is updated globally and more information evolves. If you do not have easy access to the internet then don’t forget libraries have free internet access and the staff at your local library will be delighted to help you search. References for drug food interactions

[ngfb buttons="facebook, gplus, twitter, linkedin, pinterest, stumbleupon, tumblr"]

WellBeing Clinics home


About the Author:

Derby Chiropractor Ian Reed and co founder of WellBeing Clinics Derby