Prescription Medications & Diet: Common Drug-Food Interactions That Could Endanger Your Health

Wednesday, October 11, 2006 - 1:44pm

By Michèle Turcotte, MS, RD/LDN

When taken as directed, prescription drugs can fight infections and control the symptoms of many chronic conditions. However, it's important to remember that if you take one or more prescription drugs daily, you may be at-risk for developing nutritional deficiencies. In addition, eating behaviors and certain nutrients within foods themselves can interfere with a drug's absorption, reducing or intensifying its effects. Here are just a few examples of the potential hazards of drug-food interactions:

1.   Manage you grapefruit intake whilst taking medications

Scientists have discovered that when the body digests grapefruit it uses the same liver "pathway" as many medications, including those that treat hypertension, allergies, and depression. To ensure these drugs perform their functions most effectively, avoid drinking grapefruit juice or eating grapefruit within four hours of taking your medications (particularly if these instructions are included on the label).

2.   Smoked fish, certain aged meats and cheeses, and red wine interact with certain antidepressants

These foods all have an amino acid called tyramine in common. Tyramine interacts with a certain class of antidepressants known as monoamineoxidase inhibitors (MAOIs). The interaction between MAOIs and these foods can cause serious side effects, such as nausea, headaches, and high blood pressure.

3.   Limit your intake of Vitamin K with certain prescribed drugs

People who take Coumadin, a well-known and widely prescribed blood thinning medication (prescribed for patients with heart conditions), should avoid eating large amounts of vitamin K rich foods daily. Instead consume small, steady, controlled amounts of these foods throughout the week. Your body manufactures some vitamin K (a fat-soluble vitamin that promotes blood clotting). Vitamin K rich foods include broccoli and dark green, leafy vegetables (e.g. kale, spinach, and sea vegetables). Because these are very nutritious foods, do not exclude them completely from your diet. Dietary restrictions depend upon dosage and other factors.

4.   Acidic foods and beverages should not be consumed at the same time as antibiotics

Acidic foods and beverages-such as tomato sauce, tea, coffee, and citrus juices-can destroy penicillin in the body (the most commonly prescribed antibiotic), so avoid taking them at the same time. "Cycline" antibiotics (e.g. tetracycline) should not be taken within two hours of consuming dairy products because calcium may block the absorption of this medication1.

5.   Diuretics can deplete your potassium stores

Diuretics may be prescribed for those with hypertension, congestive heart failure, and other conditions in order to remove excess fluid from the body. Some diuretics are not "potassium sparing," meaning the diuretic may deplete this mineral from the body. Consume potassium-rich fresh or frozen fruits and vegetables, and inquire about switching to a potassium sparing diuretic, if possible. Even potassium-sparing diuretics can deplete your body of other important minerals, such as magnesium and zinc. Make sure that your multivitamin supplement contains at least 100mg of magnesium and ask your doctor about taking additional magnesium supplements. Eat foods rich in zinc and magnesium such as shrimp, whole grains, and nuts and seeds.

Always consult your doctor about food-drug interactions

When in doubt always ask your physician, pharmacist or registered dietitian about food-drug interactions, dosage information and side effects. Make sure you understand how to take the prescription at the time of purchase. And pay attention to the written material and stickers that accompany your medication because dosage recommendations and/or dietary considerations are included.

1Note: Oral contraceptives enhance the body's absorption of calcium. However, they may interfere with the body's ability to absorb folic acid (a very important nutrient, especially for women of child-bearing age to prevent the birth defect spina bifida). Spinach and fortified breads and cereals are excellent sources of folic acid.