Yaiza de la Campa. Journalist
All pharmacology manuals include a chapter on drug interactions which explains if medicine should be taken in spaced doses, and if so, which ones. There's also information about drugs that change the way certain nutrients are absorbed or cause digestive disorders that lead to malnutrition. But it's unusual to find information about how foods impact the effects of medicines, whether they enhance, reduce, or even block drug action.
A document drafted by the Ministry of Health in 2011 warns that interaction between drugs and food can negatively affect a treatment's safety and effectiveness as well as the patient's nutritional status. However, those interactions can be prevented through a coordinated effort by the team of healthcare professionals: the doctor, pharmacist, nutritionist, and nurse.
What foods or nutrients impact the effects of medicines?
Those that block absorption of a medicine:
Proteins: interfere with the absorption of L-DOPA, which is used to treat Parkinson's disease. As a result, it is ideal to eat nutrients (meat, fish, eggs, dairy products and legumes in particular) for dinner only.
Vitamin K: found in cabbage, beets, lettuce, green tea, spinach, peas, chard, broccoli, brussel sprouts, and also in the liver; it limits the effectiveness of oral anticoagulants.
Fats: diminish the effectiveness of drugs used to treat AIDS (Zidovudine, Indinavir and Didanosine). Like vitamin K-rich foods, fats also reduce oral anticoagulants' mechanism of action. One option is to take these drugs on an empty stomach.
Dairy products: reduce the absorption and effectiveness of certain medicines, such as antibiotics (Tetracyclines) and oral penicillins. They also block the absorption of iron supplements, which are often prescribed to treat anemia and during pregnancy, and of laxatives which contain magnesium. To this end, it is recommended to let at least two hours elapse between taking the medicine and eating dairy.
Those that inhibit drug action:
Licorice: blocks the action of certain antihypertensives, such as diuretics and beta-blockers.
Soy: impedes the action of Tamoxifen, an anti-estrogen drug for preventing breast cancer.
Tea: its high tannin content impedes the absorption of iron supplements.
Very hot foods.
Enhance drug action.
Garlic: an abundance in the diet strengthens the action of oral anticoagulants (Warfarin and Acenocoumarol), which increases the risk of haemorrhages and bleeding.
Orange juice: increases the absorption of iron supplements to treat anemia and taken during pregnancy. It has a positive effect.
The following have adverse effects when combined with certain drugs:
Grapefruit juice: produces toxicity when mixed with many drugs, such as those used to treat hypertension, transplant anti-rejection medications, antihistamines and cholesterol meds.
Soy: produces toxicity when consumed with Haloperidol (to treat central nervous system diseases) and Warfarin.
Mature cheeses: Tyramine (present in cheddar, blue, gorgonzola, camembert and brie cheese, as well as in beer, smoked meats and processed meats, red wine, and foods that are pickled, preserved, marinated and fermented) reacts with antidepressants, such as MAO inhibitors, which leads to vasoconstriction, hypertensive crises, severe headaches, nausea and heart palpitations.
The following diminish drug action:
Garlic: reduces the plasma levels of Saquinavir, which is used to treat HIV.
As a general rule, the more fatty, caloric and hot our food, the slower the digestion and the longer it takes for a drug to be effective.
Source: Interacciones alimento/medicamento. Inf Ter Sist Nac Salud 2011; 35: 3-12.