The interaction between drugs, food and health


Many people take drugs for their health problems, and do not realise that drugs can affect the body’s ability to absorb nutrition from food. Some foods can also interfere with the activity of drugs. After reading the information set out below you may be concerned about medication you are taking, but it is important to consult your medical practitioner before stopping any prescribed medication.

Effect Of Drugs In Nutritional Terms

Drugs can affect your absorption of nutrition from your food in several different ways.

Some drugs cause gastric irritation, (e.g. aspirin and non-steroidal anti-inflammatory drugs). These should be taken with food to minimise this problem.

Some drugs change gastrointestinal pH. For example, antacids neutralise stomach acids and so reduce vitamin B12 absorption.

Some drugs change gastrointestinal motility, particularly laxatives. ‘Gastrointestinal motility’ is the medical term for how fast food moves through the stomach and intestine. If food moves more quickly through the intestine, it may be difficult for the body to extract all the nutrients it needs. Aluminium, which is in many antacids, has a relaxing effect on some muscles and so slows the process down – good for nutrient absorption, but can cause other problems.

Some drugs form insoluble complexes with components of food; this means that neither the drug nor the nutrient (usually a mineral) will be absorbed. For example, tetracyclines bind to calcium in dairy products.

Some drugs affect nutrient metabolism and distribution. For example, anti-convulsive drugs affect folic acid metabolism; aspirin competes with folate for binding sites on serum proteins.

Some drugs affect nutrient excretion, causing more or less of a particular nutrient to be excreted. For example, corticosteroids increase excretion of potassium and increase retention of sodium; diuretics may increase the excretion of potassium, magnesium, calcium and the water-soluble the B vitamins and vitamin C.

Some drugs affect the bowel flora. Our intestine contains million of useful bacteria that produce some vitamins and contribute to proper digestion and a healthy immune system. There are also other harmful bacteria that can compete with the good bacteria. Antibiotics lead to a reduction of the beneficial bacteria. If you have been taking antibiotics, I strongly recommend you take some probiotics to repopulate your gut with the healthy bacteria.

Some drugs can lead to changes in appetite. For example, anti-convulsant drugs can cause diarrhoea and reduce appetite.

Steroid drugs have the potential to interfere with the absorption and utilisation of calcium, potassium, sodium, protein, and vitamins C and D. Aspirin has been reported to lower plasma vitamin C concentrations, but how it does this is not known.

Effect Of Food On Drugs

Some foods affect drug absorption and use. This is usually set out in the leaflet that comes with the drug. Examples include:

  • Garlic can affect anticoagulants and diabetes medication.
  • Garlic and ginkgo biloba can affect anticoagulants.
  • Grapefruit can cause the body to absorb more of some drugs such as antihistamines, statins, benzodiazepines.
  • St John’s Wort may affect the contraceptive pill and the antidepressant Prozac.
  • Alcohol interacts with some drugs particularly those that have an effect on the brain, e.g. sleeping pills, antidepressants.
  • Over-ripe cheese, pickles, some beers and red wine can affect MAO antidepressants, leading to a dangerous rise in blood pressure.
  • Cranberry juice can affect Warfarin.