Antacids (containing calcium or aluminium) may decrease the absorption of the supplemental iron, vitamins A, E, D, K and folate . H2 blockers (ranitidine) and proton pump inhibitors (omeprazole) decrease stomach acidity (hypochlorhydria), which may decrease the absorption of vitamin B12, iron and calcium [5,15,16,24].
Sulfonamides, such as sulfamethoxazole, may decrease the bioavailability of folate .
Tetracycline can reduce the absorption of calcium .
The anticoagulant warfarin may decrease the absorption of vitamin K .
Anticonvulsants, such as phenobarbital or phenytoin, may decrease the levels of folate and vitamin D [1,6,7].
ACE inhibitors, such as captopril, may cause a mild increase of blood potassium levels (hyperkalemia) [9,14].
Antimalarics, such as pyrimethamine, may lower folate levels .
The antituberculosis drug rifampin may lower the levels of vitamin D .
Barbiturates can decrease folate bioavailability .
Beta-blockers, such as propranolol, can decrease blood glucose levels .
Birth control pills may decrease vitamin B6 bioavailability .
Chemotherapeutics, such as cisplatin, may decrease the absorption of several nutrients .
Cholestyramine may decrease the absorption of vitamins A, B12, D, E and K and folate, and calcium [6,22].
Corticosteroids (cortisol, prednisone) may decrease the levels of vitamin B6, D and K, calcium, potassium, selenium and chromium [1,23,24], increase blood glucose levels and cause water and sodium retention .
Diuretics, such as furosemide or hydrochlorothiazide, can stimulate the excretion of potassium, and magnesium [1,6,9].
Fat-blocking weight loss drugs, like orlistat, may decrease the absorption of fat soluble vitamins A, D, E and K .
Digoxin can derange blood potassium levels .
Laxatives (any type) may hamper the absorption of fat soluble vitamins A, D, E and K and other nutrients and stimulate the excretion of potassium and water [1,6].
Lithium can impair the iodine uptake or its release from the thyroid gland .
MAO inhibitors, such as isocarboxazid and phenelzine, taken together with foods high in tyramine (aged cheeses, red wine, sausage, liver, pickled herring, brewer’s yeast, fava beans) may cause severe headache or marked increase in blood pressure .
Methotrexate may affect the effectiveness of folate and vitamin B12 in the body [6,11].
Statins (cholesterol-lowering drugs), like lovastatin, may decrease the amount of Coenzyme Q10 in the body .
NUTRIENTS That Can Affect Drug Absorption
Calcium from milk or supplements can greatly decrease the absorption of the antibiotic tetracycline  and bisphosphonates (for osteoporosis) .
Foods high in vitamin K (broccoli, Brussels sprouts, kale, parsley, spinach) when consumed in large amounts, may decrease the absorption of the anticoagulant warfarin .