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.

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.

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!

Appetite Boosters

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.

Alcohol

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:

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:

Source: From the PDR® Family Guide to Nutrition and Health™