Sometimes the combinations of interacting foods and drugs are positively astounding. Or, as the next paragraph suggests, breathtaking. Here’s a prime example. Everyone knows that people with asthma may find it hard to take a deep breath around the barbecue. The culprit’s the smoke, right? Yes. And no.

True: Breathing in smoke irritates air passages. But the kicker is that eating charcoal-broiled food speeds the body’s elimination of theophylline, a widely used asthma drug, reducing the drug’s ability to protect against wheezing. Take the drug, eat the food, and end up wheezing. Yipes. Another potential troublemaker is fruit juice. Acidic beverages (colas as well as fruit juice) can send the antibiotics erythromycin, ampicillin, and penicillin down for the count.

Grapefruit juice is another acidic actor. In the mid-1990s, researchers tracking the effects of alcohol beverages on the blood pressure drug felodipine (Plendil) tripped across the Grapefruit Effect, a dramatic reduction in your ability to metabolize and eliminate certain drugs.

Grapefruit juice contains substances that suppress the effectiveness of CYP 3A4, an intestinal enzyme required to convert many drugs to water-soluble substances you can flush out of your body; without the enzyme, you can’t get rid of the drug. The result may be an equally dramatic rise in the amount of medication in your body, leading to unpleasant side effects.

The list of drugs that interact with grapefruit juice has now expanded beyond felodipine to include a second blood pressure med, nifedipine (Adalat, Procardia), plus — among others — the cholesterol-lowering drugs lovastatin (Mevacor), pravastatin (Pravachol), and simvastatin (Zocor); the antihistamine loratadine (Claritin); the immunosuppressant drug cyclosporine; and saquinavir (Invirase), a protease (enzyme) inhibitor used to treat HIV.

By the way, if you feel particularly wired after drinking grapefruit juice with your a.m. coffee or tea, maybe it’s because the juice also interacts with caffeine. Who knew? Water pills, more properly known as diuretics, make you urinate more often and more copiously, thus increasing your elimination of the mineral potassium.

To make up what you lose, experts suggest adding potatoes, bananas, oranges, spinach, corn, and tomatoes to your diet. Consuming less sodium (salt) while you’re using water pills makes the water pills more effective and decreases your loss of potassium.

Oral contraceptives seem to reduce the ability to absorb B vitamins, including folate. Taking lots of aspirin or other NSAIDs (nonsteroidal anti-inflammatory drugs) such as ibuprofen can trigger a painless, slow but steady loss of small amounts of blood from the lining of your stomach that may lead to irondeficiency anemia.

Persistent use of antacids made with aluminum compounds may lead to loss of the bone-building mineral phosphorus, which binds to aluminum and rides right out of the body. Laxatives increase the loss of minerals (calcium and others) in feces. The antiulcer drugs cimetidine (Tagamet) and ranitidine (Zantac) can make you positively giddy.

These drugs reduce stomach acidity, which means the body absorbs alcohol more efficiently. According to experts at the Mayo Clinic, taking ulcer medication with alcohol leads to twice the wallop, like drinking one beer and feeling the effects of two.

The point, of course, is to read the label and definitely check with your doctor or pharmacist for any potential food and drug interactions whenever you take medication. Finally, consider nutritional supplements.

The vitamins and minerals in nutritional supplements are simply food reduced to its basic nutrients, so interactions between drugs and supplements aren’t a surprise. Table below lists some common vitamin/mineral and drug interactions.

You Absorb Less	When You Take
Vitamin A	Aluminum antacids Bisacodyl (laxative) Cholestyramine (lower cholesterol) Fenfluramine (diet pill) Mineral oil (laxative) Neomycin (antibiotic)
Vitamin D	Bisacodyl (laxative) Cholestyramine (lowers cholesterol) Mineral oil (laxative) Neomycin (antibiotic)
Vitamin K	Bisacodyl (laxative) Cholestyramine (lowers cholesterol) Mineral oil (laxative) Neomycin (antibiotic)
Vitamin C	Aspirin Barbiturates (sleeping pills) Cortisone and related steroid drugs
Thiamin	Antacids (calcium) Aspirin Cortisone and related steroid drugs
Riboflavin	Birth control pills
Folate	Aspirin Cholestyramine (lowers cholesterol) Penicillin Phenobarbital, primidone, phenothiazines (antiseizure drugs) Sulfa drugs
Vitamin B12	Cholestyramine (lowers cholesterol) Neomycin (antibiotic)
Calcium	Cortisone and related steroid drugs Diuretics (water pills) Magnesium antacids Neomycin (antibiotic) Phosphorus laxatives Tetracycline (antibiotic)
Phosphorus	Aluminum antacids
Magnesium	Amphotericin B (antibiotic) Diuretics (water pills) Tetracycline (antibiotic)
Iron	Aspirin and other nonsteroidal anti-inflammatory drugs Calcium antacids Calcium supplements (with meals) Cholestyramine (lowers cholesterol) Neomycin (antibiotic) Penicillin (antibiotic) Tetracycline (antibiotic)
Zinc	Diuretics (water pills)

James J. Rybacki, The Essential Guide to Prescription Drugs 2002 (New York: Harper Collins, 2001); Brian L. G. Morgan, The Food and Drug Interaction Guide (New York: Simon and Schuster, 1986); Eleanor Noss Whitney, Corinne Balog Cataldo, and Sharon Rady Rolfes, Understanding Normal and Clinical Nutrition, 4th ed. (Minneapolis/St. Paul: West Publishing, 1994)