By Adrienne Youdim, MD, FACP

Nutrition can affect the body’s response to drugs; conversely, drugs can affect the body’s nutrition.


Foods can enhance, delay, or decrease drug absorption. Foods impair absorption of many antibiotics. They can alter metabolism of drugs; eg, high-protein diets can accelerate metabolism of certain drugs by stimulating cytochrome P-450. Eating grapefruit can inhibit cytochrome P-450 34A, slowing metabolism of some drugs (eg, amiodarone, carbamazepine, cyclosporine, certain calcium channel blockers). Diets that alter the bacterial flora may markedly affect the overall metabolism of certain drugs.


Some foods affect the body’s response to drugs. For example, tyramine, a component of cheese and a potent vasoconstrictor, can cause hypertensive crisis in some patients who take monoamine oxidase inhibitors and eat cheese.


Nutritional deficiencies can affect drug absorption and metabolism. Severe energy and protein deficiencies reduce enzyme tissue concentrations and may impair the response to drugs by reducing absorption or protein binding and causing liver dysfunction. Changes in the GI tract can impair absorption and affect the response to a drug. Deficiency of calcium, magnesium, or zinc may impair drug metabolism. Vitamin C deficiency decreases activity of drug-metabolizing enzymes, especially in the elderly.


Many drugs affect appetite, food absorption, and tissue metabolism (see Table: Effects of Some Drugs on Appetite, Food Absorption, and Metabolism). Some drugs (eg, metoclopramide) increase GI motility, decreasing food absorption. Other drugs (eg, opioids, anticholinergics) decrease GI motility. Some drugs are better tolerated if taken with food.

Effects of Some Drugs on Appetite, Food Absorption, and Metabolism



Increases appetite

Alcohol, antihistamines, corticosteroids, dronabinol, insulin, megestrolacetate, mirtazapine, many psychoactive drugs, sulfonylureas, thyroid hormone

Decreases appetite

Antibiotics, bulk agents (methylcellulose, guar gum), cyclophosphamide, digoxin, glucagon, indomethacin, morphine, fluoxetine

Decreases absorption of fats


Increases blood glucose levels

Octreotide, opioids, phenothiazines, phenytoin, probenecid, thiazide diuretics, corticosteroids, warfarin

Decreases blood glucose levels

ACE inhibitors, aspirin, barbiturates, beta-blockers, insulin, monoamine oxidase inhibitors (MAOIs), oral antihyperglycemic drugs, phenacetin, phenylbutazone, sulfonamides

Decreases blood lipid levels

Aspirin and p -aminosalicylic acid, lasparaginase, chlortetracycline, colchicine, dextrans, glucagon, niacin, phenindione, statins, sulfinpyrazone, trifluperidol

Increases blood lipid levels

Adrenal corticosteroids, chlorpromazine, ethanol, growth hormone, oral contraceptives (estrogen-progestin type), thiouracil, vitamin D

Decreases protein metabolism

Chloramphenicol, tetracycline

Certain drugs affect mineral metabolism (see Table: Possible Effects of Drugs on Mineral Metabolism). Certain antibiotics (eg, tetracyclines) reduce iron absorption, as can certain foods (eg, vegetables, tea, bran).

Possible Effects of Drugs on Mineral Metabolism



Diuretics, especially thiazides, and corticosteroids

Can deplete body potassium*

Laxatives if used repeatedly

May deplete potassium*

Cortisol, desoxycorticosterone, and aldosterone

Cause marked sodium and water retention, at least temporarily

Sulfonylureas and lithium

Impair uptake or release of iodine by the thyroid

Oral contraceptives

Lower blood zinc levels, increase copper levels

Certain antibiotics (eg, tetracyclines)

Reduce iron absorption

*Depletion of potassium increases susceptibility to digoxin-induced cardiac arrhythmias.

Retention of sodium and water is much less with prednisone, prednisolone, and some other corticosteroid analogs.

Certain drugs affect vitamin absorption or metabolism (see Table: Possible Effects of Drugs on Vitamin Absorption or Metabolism).

Possible Effects of Drugs on Vitamin Absorption or Metabolism




Impairs thiamin utilization


Interferes with niacin and pyridoxine metabolism

Ethanol and oral contraceptives

Inhibit folate absorption

Phenytoin, phenobarbital, primidone, or phenothiazines

In most patients, cause folate (folic acid) deficiency*, probably because hepatic microsomal drug-metabolizing enzymes are affected


Can cause vitamin D deficiency

Aminosalicylic acid, slow-release potassium iodide, colchicine, trifluoperazine,metformin, ethanol, and oral contraceptives

Interfere with absorption of vitamin B12

Oral contraceptives with a high progestin dose .

Can cause depression, probably because of metabolically induced tryptophan deficiency

Proton pump inhibitors

Can cause deficiencies of vitamin B12, vitamin C, iron, calcium, and magnesium

*Folate supplements may make phenytoin less effective.