Food and drug interactions

Food/ food components and nutritional supplements can interfere with drug absorption, especially if the drug is taken orally.

Common causes of drug malabsorption:

  • Polypharmacy (the concurrent use of multiple medications by patients); the risk of a food-drug interaction increases with the number of medications taken. g. taking metformin, glipizide, levothyroxine, Lipitor, Diovan, fluoxetine all at the same time renders the body unable to absorb the drug thus limiting its effectiveness to treat that certain illness.
  • Age is a major contributing factor in adverse effects of food and drug interactions, especially affecting the elderly, as they are likely to be taking many drugs (prescription and over the counter medication).
  • Gender women usually have more fat, which alters drug distribution
  • Genetics affect drug metabolism
  • Nutritional status (e.g.: poor protein status)

Common food/nutrient effects on drugs:

  • Grapefruit/ grapefruit juice contains an enzyme that inhibit the absorption of many oral medications.

Some medications affected by this fruit include:

  1. Anti-hypertensives (filodipine, nifedipine, nimodipine, nicardipine, isradipine)
  2. Immunosuppressants (cyclosporine, tacrolimus)
  3. Antihistamines (astemizole)
  4. ARVs/ Protease inhibitors (Indinavir, saquinavir)
  5. Lipid-Lowering Drugs (atorvastatin, lovastatin, simvastatin)
  6. Anti-anxiety, anti-depressants (buspirone, diazepam, midazolam, triazolam, zaleplon, carbamazepine, clomipramine, trazodone
  • Iron supplements are best absorbed when taken with water on an empty stomach. For best iron absorption avoid; bran, eggs, fibre supplements, tea, coffee, dairy products and calcium supplements.
  • Dairy products such as milk, yoghurt and cheese decrease the absorption of antibiotics.
  • Alcohol affects diabetic pills which may lead to very low blood sugar. Also taking mild pain reliever drugs with alcohol may cause severe liver damage and cause increased drowsiness.

Make sure that drug absorption inhibiting foods are eating at least 4-5 hours before or after taking the drug


Such food should be completely avoided in the duration of the treatment course if possible.