Drug-Food Interactions: Foods to Watch Out For When Taking Medication

Take three times daily with meals. . . . Do not take with dairy products. . . . Avoid alcoholic beverages. You’ve probably seen instructions like these many, many times on your prescription and over-the-counter medications. They are telling reminders that food and medicine can interact in numerous unsuspected ways. Some foods can reduce a medication’s effectiveness; others may make it more effective (and possibly, even harmful). Likewise, certain medicines can undermine good nutrition, especially in people who had nutritional problems to start with.

Although some food/drug interactions may be quite dangerous, most don’t produce any sudden or dramatic symptoms. However, they can cause bothersome side effects and minor nutritional deficiencies—problems that often go unrecognized, according to Jeffrey B. Blumberg, Ph.D., professor of nutrition at Tufts University. “People may take a drug that doesn’t seem to work—or that causes lethargy, irritability, confusion, or other symptoms—and then blame the drug or just old age,” he says. “But the actual problem may be something like a drug-induced vitamin deficiency that could be easily corrected.”

Doctors have trouble predicting when many of these interactions will occur. Scientists still have a lot to learn about how food and drugs affect each other and about the way the body uses trace nutrients—substances such as iron, zinc, and copper that are vital to health in very small amounts. These trace nutrients can also be affected by medicine.

Food/drug interactions also tend to be unpredictable because individuals vary considerably in their response to a particular medication, and because no two people eat exactly the same diet. We do know, however, that for some people the chance of a troublesome interaction is higher. Among those at greatest risk:

The elderly, who are most likely to be taking one or more types of medication and have other health and nutrition problems
Heavy drinkers
People with liver or kidney disorders
People who do not eat an adequate or balanced diet
Men and women on special, restricted diets
People with cancer
People who have diseases of the stomach and intestines
Pregnant and nursing women

If you are in any of these groups, make a special point of asking your doctor or pharmacist about food/drug interactions when you get a prescription for a new medication. And don’t forget that the “over-the-counter” medications that you buy without a prescription—aspirin and antacids, for example—may also interact with food. Watch out for alcohol, too. It interacts badly with a large number of medicines.


Food/Drug Interactions That Can Cause Serious Harm

Most food/drug interactions do not have the potential for serious or permanent damage. But these do:
Potassium-rich food plus amiloride (Moduretic) or triamterene (Diazide, Dyrenium, Maxzide)
Taken together, they can result in toxic levels of potassium.
Grapefruit juice plus felodipine (Plendil) or pimozide (Orap)
This combination may result in dangerously high concentrations of the drug’s active ingredient and possibly lead to heart rhythm problems.
Tyramine-containing foods plus furazolidone (Furoxone), isocarboxazid (Marplan), linazolid (Zyvox), phenelzine (Nardil), selegiline (Eldepryl), or tranylcypromine (Parnate)
May cause dangerously high blood pressure.
Insulin and alcohol
This combination may cause a rapid worsening of low blood sugar (hypoglycemia).
Source: Red Book Database, Medical Economics


How Food Affects Medicine

One factor couldn’t be simpler: it’s merely the amount of food in your stomach when you take your medicine. The size and composition of a meal can influence the amount of medicine absorbed and the time it takes to reach the bloodstream. Many drugs are most effective on an empty stomach, with nothing to interfere with the breakdown of the medicine or slow its delivery to the rest of the digestive tract.

However, doctors recommend taking many medications with meals for several reasons. Mealtimes provide an easy reminder to take several doses a day. Some medicines—aspirin or nonsteroidal anti- inflammatory drugs such as Advil or Nuprin, for example—can irritate the stomach lining unless they are buffered by food. Other drugs—including blood pressure-lowering medications such as clonidine (Catapres) and reserpine (Serpasil), and water pills such as chlorothiazide (Diuril)—actually work better on a full stomach.

But, while a meal can protect the stomach from some drugs and boost the potency of others, some of the things you eat can cause problems with certain medications. Difficulties with absorption head the list.

The calcium in dairy products, for instance, binds to and inhibits the absorption of several drugs, including iron and antibiotics such as tetracycline and Cipro. As a result, less medicine is absorbed, and it may not work. If you need to take tetracycline, Cipro, or iron (by itself or as part of a multivitamin), take your doses at least two hours before or after eating any dairy products or calcium-containing supplements or antacids.

Fosamax, a medication used to treat osteoporosis, is drastically affected by food. It must be taken first thing in the morning, before the first food, beverage, or medication of the day. Even coffee and orange juice can impede the absorption of Fosamax.

Olestra, a fat substitute found in potato chips, crackers, and other snacks, inhibits the absorption of vitamins and other nutrients. Food manufacturers who use Olestra are required to add vitamins A, D, E, and K to the food. Given this known problem with absorption, it’s probably not a good idea to take your medicine shortly before or after eating a snack made with Olestra, although no specific warnings are listed on the label.

Be Careful of Breakfast Beverages

The coffee and grapefruit juice you enjoy as part of your morning routine can cause problems if they are taken with certain medications.

Caffeine is an active ingredient in over-the-counter products intended to help you stay awake (such as No-Doz) and in pain medications such as Excedrin, Fiorinal, and Midol. The extra caffeine from a coffee or cola can cause symptoms of caffeine overdose, such as nervousness, excitability, rapid heartbeat, and headache. It’s also wise to avoid caffeine if you take monoamine oxidase inhibitors, since the combination can raise your blood pressure too high.

A glass of grapefruit juice is a healthy way for most people to start the day, but if you take certain medications, it could mean trouble! Grapefruit juice can interfere with the way certain medicines are absorbed and utilized in the body, possibly leading to dangerously high concentrations of drug. Examples of medications that should not be taken with grapefruit juice include: Crixivan, Halcion, Lexxel, Neoral, Orap, Plendil, Pletal, Prograf, Quinaglute, SangCya, and Xanax.


These Drugs and Caffeine Don’t Mix

Medicine Reaction
Caffeine-containing medications such as Excedrin, Fiorinal, and Midol Symptoms of caffeine overdose
Caffeine pills such as No-Doz Symptoms of caffeine overdose
MAO inhibitors such as Nardil and Parnate Excessive blood pressure
Fosamax Decreased absorption of Fosamax


MAO Inhibitor Means Caution

Some foods contain substances that react chemically with the active ingredients in certain drugs, making them more or less potent or even toxic. A prime example is the potentially deadly interaction between a food ingredient called tyramine and a class of drugs called the monoamine oxidase (MAO) inhibitors, which are prescribed for depression and, sometimes, for Parkinson’s Disease. These drugs include the antidepressants isocarboxazid (Marplan), phenelzine (Nardil), and tranylcypromine (Parnate), as well as the Parkinson’s drug selegiline (Eldepryl).

If you are taking these drugs, you must be careful to avoid all foods containing tyramine, including such items as hard cheese and aged soft cheeses, liver, pickled herring, yogurt, Chianti wine, and salami. (For more tyramine containing foods, see nearby box.) If you eat any of these foods while taking MAO inhibitors, your blood pressure could sky-rocket, creating the risk of a stroke or even death. (MAO inhibitors also react badly with many other drugs. Make sure each doctor who treats you—and even your dentist—knows that you are taking an MAO inhibitor before prescribing any other medicines.)


Foods and Beverages Containing Tyramine

Avoid these selections if you are taking one of the antidepressant drugs such as Marplan, Nardil, or Parnate, the Parkinson’s medication Eldepryl, the antibiotic Zyvox, or the infectious diarrhea remedy, furazolidone (Furoxone).
Cheeses (except cream cheese, cottage cheese, and ricotta)
Sour cream
Homemade yogurt (Store-bought yogurt is all right.)
Smoked or pickled fish, such as herring
Fermented sausages (salami, bologna, pepperoni, summer sausage)
Brewer’s yeast
Canned or overripe figs
Fava beans, broad beans (You may eat string beans and baked beans.)
Fermented or aged foods
Soy sauce
Red wine, Chianti, sherry
Beer (including alcohol-free beer)
Clear spirits or white wines may be safe in moderation; ask your doctor how much, if any, is an acceptable amount. Your physician may also advise you to cut down or eliminate coffee, tea, and soft drinks containing caffeine; and to avoid such nonprescription medicines as cold or allergy pills and diet pills.

Adapted from: The Over-50 Guide to Psychiatric Medications, 1989.


Beware Licorice and Onions

Eating a lot of natural licorice, or taking herbal remedies that contain licorice, may interfere with the action of high blood pressure drugs, such as water pills. Licorice contains a substance that can cause the body to retain sodium; and this can push blood pressure up to unhealthy levels. Most licorice sold in the U.S. is artificially flavored, but some imported candies may contain the real thing.

The clot-preventing drug warfarin (Coumadin) may become too powerful—possibly causing bleeding problems—if you eat a lot of onions. Conversely, if you load up on foods rich in vitamin K (including green leafy vegetables such as spinach and Brussels sprouts) you might defeat the effectiveness of these anticoagulant drugs, because vitamin K promotes blood clotting.

Potassium: A Balancing Act

If you take drugs to lower blood pressure, it pays to keep an eye on potassium intake. This mineral may be affected by so-called water pills: thiazide diuretics such as hydrochlorothiazide (HydroDIURIL), and other diuretics such as furosemide (Lasix) and bumetanide (Bumex). These drugs help lower blood pressure by flushing out fluid and sodium, but they may also get rid of too much potassium, which is essential to the functioning of heart and muscles. Eating plenty of potassium-containing foods such as bananas and orange juice, often prevents depletion. Your doctor may also wish to test your potassium level, and might prescribe supplements if necessary.

On the other hand, some blood pressure medications do exactly the opposite, acting to block potassium loss. They include so-called “potassium-sparing” diuretics (Aldactone, Dyazide, Moduretic,) and “ACE inhibitors” (Capoten, Prinivil, Vasotec). With these drugs, the danger is an accumulation of too much potassium, which can slow the heart, leading to weakness and even shock. If your physician prescribes one of these drugs, avoid using potassium supplements or salt substitutes containing potassium. Moderate amounts of potassium-containing foods, however, are safe.


Some Drugs That Can Cause Nutritional Deficiencies

Drugs Deficiency
Birth control pills and estrogen-replacement therapy Folic acid, vitamin B6
Certain water pills Magnesium, potassium
Isoniazid Niacin, vitamin B6
Questran Vitamins A, B12, D, E, and K
Seizure drugs and sedatives Calcium, folic acid, vitamins D and K
Steroid medications Vitamins B6, C, and D
Xenical Vitamins A, D, E, and K


How Drugs Affect Nutrition

A number of common prescription and nonprescription drugs can sabotage good nutrition. People who must take drugs at high doses or for extended periods are at highest risk. The drugs can erode nutrition in several ways.

Tough On the Taste Buds

Some medications can alter the sense of taste, either blunting flavors or making some foods taste different or “off.” Among the drugs that may have this effect are penicillin, an antifungal medication called griseofulvin (Fulvicin, Grifulvin), the cholesterol-lowering drug cholestyramine (Questran), and medications used in chemotherapy for cancer.

Many other medicines can cause dry mouth, making it difficult and unpleasant to chew and swallow. These include some allergy drugs (antihistamines), high blood pressure medications, and antidepressants.


Some Foods That Interfere with Drugs

Foods Drugs
Dairy products Tetracycline
High-sodium foods Diuretics
High-fiber foods Digitalis
High-protein foods L-dopa
Leafy vegetables Warfarin
Soybeans, cabbage, kale Thyroid hormone


Appetite Beaters

There is a long list of drugs that cause digestive upset, including pain killers, estrogen preparations, and cholesterol-lowering medications. Some drugs take the edge off the appetite; others can make you feel miserable—nauseated, bloated, and gassy.

Constipation or diarrhea are other common causes for a loss of appetite, especially in older people. Among the drugs causing constipation are codeine, morphine, and iron supplements. If you are taking powerful painkillers, ask your doctor about using a stool softener or other preventive.

If you experience any digestive symptoms or just find yourself losing weight—especially after starting a new medication—tell your doctor. The answer may be as simple as changing the amount or timing of your dosage, or switching to a different medication in the same category. But don’t try such experiments on your own, particularly with prescription drugs!

Physicians prescribe some drugs deliberately to suppress appetite for purposes of weight control. However, using appetite-controlling drugs on a long-term basis is controversial and can be dangerous. A healthy diet and exercise are the keys to weight loss; ask your doctor before taking any over-the-counter appetite suppressants.

Appetite Boosters

Some drugs stimulate appetite to such an extent that overeating becomes a temptation. These include blood-sugar-lowering medications for diabetes such as chlorpropamide (Diabinese), glipizide (Glucotrol), glyburide (Micronase), and tolbutamide (Orinase). Antidepressants and high doses of corticosteroid drugs may also trigger hunger pangs.

Absorption Problems

Certain drugs can cut down on the body’s ability to extract nutrients from food in the same way as some foods can keep drugs from being properly absorbed. Antacids containing aluminum and calcium can keep the intestines from absorbing phosphorus, a mineral vital to healthy bones and teeth. Antacids can also impair the body’s use of thiamin (vitamin B1) and iron.

Both the antibiotic neomycin and certain other drugs, such as cholestyramine (Questran), impair the absorption of fat-soluble vitamins (for example, A, D and K.) Cholestyramine may also decrease the absorption of folate, cobalamin, iron, calcium, and magnesium.

Xenical (orlistat), a weight-loss medication, works by decreasing the amount of fat absorbed from your diet. Unfortunately, that means that it also diminishes absorption of the fat-soluble vitamins and beta carotene. If you take Xenical, you should also take a supplement that contains the vitamins A, D, E, and K and beta carotene.

The chronic use of laxatives may also affect absorption, especially when the laxatives act by irritating the lower intestines. The active ingredient in Ex-Lax can cause diarrhea; and people who use this product for extended periods of time may develop deficiencies in vitamin D and calcium. They may also run low on potassium as a result of losing a large amount of fluid in a short time. If you are troubled with constipation, ask your doctor about diet changes and fiber supplements that can help. To avoid becoming dependent on laxatives, use them sparingly and only as a last resort.

Certain drugs may include substances, such as the sodium found in many antacids and some forms of penicillin, that you may wish to avoid or eliminate from your diet. Some people are allergic to the inactive ingredients used in pills or capsules (starches, flavors, or coloring agents) and may need to take their drugs in a different form.


Interaction Quick Reference

Taking this drug . . . with these foods . . . Can lead to:
Achromycin (tetracycline) Dairy products Reduced effectiveness of medicine
Altace (ramipril) Salt substitutes containing potassium Heart rhythm problems
Larodopa (levodopa) High-protein foods
(meat, fish, eggs)
Reduced effectiveness of medicine
Capoten (captopril) Salt substitutes containing potassium Heart rhythm problems
Coumadin (warfarin) Foods high in vitamin K
(leafy green vegetables)
Reduced effectiveness of medicine
Foods high in vitamin E
(boiled or fried onions)
Bleeding problems
Declomycin (demeclocycline) Dairy products Reduced effectiveness of medicine
Dyazide (triamterene) Salt substitutes containing potassium Heart rhythm problems
Eldepryl (selegiline) Tyramine-containing foods Dangerously high blood pressure
Isoniazid Tuna, sauerkraut, yeast extract Headache, palpitations, flushing, sweating, itching, diarrhea
Marplan (isocarboxazid) Tyramine-containing foods Dangerously high blood pressure
Maxzide (triamterene) Salt substitutes containing potassium Heart rhythm problems
Moduretic (amiloride) Salt substitutes containing potassium Heart rhythm problems
Nardil (phenelzine) Tyramine-containing foods Dangerously high blood pressure
Orap (pimozide) Grapefruit juice Disturbed heart rhythm
Parnate (tranylcypromine) Tyramine-containing foods Dangerously high blood pressure
Plendil (felodipine) Grapefruit juice Disturbed heart rhythm
Prinivil (lisinopril) Salt substitutes containing potassium Heart rhythm problems
Sinemet (levodopa) High-protein foods (meat, fish, eggs) Reduced effectiveness of medicine
Vasotec (enalapril) Salt substitutes containing potassium Heart rhythm problems
Zyvox (linezolid) Tyramine-containing food Dangerously high blood pressure



Few people think of alcohol as a drug; but it is. And alcohol, whether in cough syrup, wine, or any of its other forms, can interact with many different medications—sometimes in dangerous ways.

The list of medications that interact with alcohol is long, and the harmful effects are varied. To be safe, you should check with your doctor before taking alcohol with any drug. Here’s just a sampling of the problems that can develop:

Central nervous system effects ranging from drowsiness and reduced mental alertness to serious complications such as coma or even death. Examples of drugs that cause this potentially dangerous side effect when combined with alcohol include:
Antihistamines (Benadryl, Chlor-Trimeton, Dimetapp, Zyrtec, and others)
Pain medications (Darvocet, Fiorinal, Percodan, and others)
Medications for mental illnesses (Compazine, Nardil, Pamelor, Paxil, Prozac, and others)
Sedatives and tranquilizers (Ativan, Nembutal, Seconal, Valium, Xanax, and others)
Stomach irritation (aspirin)
Liver damage (painkillers such as Advil, Nuprin, and acetaminophen)
Very low blood pressure (Catapres, HydroDIURIL, Hyzaar, Lasix, nitroglycerin)
High or low blood sugar levels (Glucotrol, insulin)
Severe nausea, vomiting, and flushing (Antabuse, Diabinese, Flagyl)

Special Concerns for Children

Children, too, are at risk for food/drug interactions. Their smaller bodies may respond to fluctuations in a drug’s potency that an adult might not notice.

If your child is ill and cannot keep down food and medicine, ask the physician if there are any other formulations available (for example, a liquid instead of a pill). If a youngster regularly takes medication with meals, but illness has changed his or her regular eating patterns, check with a doctor or pharmacist before giving medication on an empty stomach, advises Leslie Hendeles, Pharm. D., professor of pharmacy and pediatrics at the University of Florida in Gainesville. This is especially important with theophylline, an asthma medication that varies widely in effectiveness depending on whether or not it is taken with food.

Children, like adults, can suffer indirect nutritional damage from drug side effects such as nausea and diarrhea. By killing the good bacteria in the intestines, antibiotics such as amoxicillin (Amoxil) frequently prescribed for middle ear infections, can cause diarrhea; and long-lasting or severe diarrhea can result in debilitating losses of fluids and minerals. “To prevent this problem, try giving your child yogurt that contains active lactobacillus cultures,” advises Hendeles. You can offer up to three servings a day, he says, but don’t give your child antibiotics within two hours of serving yogurt or other dairy foods.

What You Can Do

Food/drug interactions are almost always either manageable or avoidable. It is important to recognize the signs of a possible reaction and to call your physician immediately if you suspect a problem. Your pharmacist or a registered dietitian are also excellent sources of advice when food and medication don’t seem to mix. Working with these professionals and your doctor, it’s usually possible to work out a medication plan that combats your health problem without undermining your diet.

Variety and moderation are the keys to a good diet. People who don’t get enough calories or protein respond to drugs differently from those who are well-nourished. The problem is most serious in hospitalized or seriously ill people, but it can affect others as well, especially older people who aren’t up to preparing adequate meals. If your calorie count is too low or you eat too few nourishing foods, tell your physician before starting to take a newly prescribed medication. He may need to adjust your dosage until your nutritional status improves.

To keep food/drug interactions at bay, follow these common sense tips:

If you are taking a medication on a regular schedule with no problems, stick to that routine. If you always take your pill on an empty stomach—or a full stomach—try to avoid a sudden switch.
If you experience unpleasant new symptoms while taking any medication—even a drug you have been using for a while—ask your doctor about the possibility of side effects or interactions.
When your doctor prescribes a new medication, let him or her know what other medications you are taking, including nonprescription or herbal remedies and vitamin supplements. Also mention how much alcohol you drink.
Let your doctor know if you follow a special or restricted diet—especially one that is unusually high or low in a particular kind of food—or if you plan to begin such a diet.
Don’t forget that water is a key nutrient as well, and necessary to the proper absorption of medicine. Make sure you drink the equivalent of eight glasses of water a day, particularly in hot weather when dehydration is more likely.

Prediet Plan Editorial

Prediet Plan Editorial

Patrick Kihara is a weight loss enthusiast and fitness blogger. He holds a Bachelor's Degree in Mass Communication and Journalism and several health and fitness certifications.

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