7 Foods That Don't Mix With Prescription Drugs

Your best bet is to avoid calcium-containing foods an hour before, or two hours after, taking one of these antibiotics, Brown says.

2. Leafy greens and warfarin

Among the most well-known food-drug interactions is the anticoagulant warfarin (brand names Jantoven and Coumadin) and foods containing vitamin K, such as broccoli, cabbage, kale, spinach, swiss chard, seaweed and other leafy greens. Certain vegetable oils also contain large amounts of K. These vegetables can reduce the effectiveness of the commonly prescribed medication, thus inhibiting its ability to stop or prevent blood clotting, explains Dima Qato, an associate professor at the University of Southern California School of Pharmacy and a senior fellow at USC’s Schaeffer Center for Health Policy & Economics.

Before you ditch these foods entirely, ask your doctor whether you should avoid them (or any others) while taking warfarin, or whether you can regularly consume moderate amounts. Some experts now advise people taking warfarin to be super consistent in the amount of vitamin K they consume through food, avoiding large amounts at one time. So, “If you like salad, have it three times a week and the same amount each time,” Brown advises, and your warfarin concentration should stay steady.

3. Cured meats, soy, other tyramine-containing foods, plus MAOIs

An older class of antidepressants called monoamine oxidase inhibitors (MAOIs) can have dangerous interactions with foods that contain high levels of tyramine, an amino acid. Taking MAOIs and consuming tyramine-rich foods can lead to a high tyramine level in the body, which can trigger a sudden, dangerous increase in blood pressure. Foods that are high in tyramine include smoked and cured meats, aged cheeses, fermented foods, red wine, some draft beer, soy products (soy sauce, miso, tofu) and very ripe bananas. These days, MAOIs aren’t used as frequently to combat depression, but they are sometimes used to treat Parkinson’s disease. If you’re taking an MAOI, it’s best to avoid these foods, Brown says. You can also ask your doctor for a complete list of dietary restrictions.

4. Grapefruit and cholesterol-lowering drugs

Consuming grapefruit or grapefruit juice can inhibit an enzyme that’s necessary for statins to be metabolized, Qato cautions. As a result, “the drug stays in the blood and accumulates, increasing the risk of side effects such as muscle pain.”

Of the statins, atorvastatin, lovastatin and simvastatin (common brand names Lipitor, Altoprev/Mevacor and Zocor) are the most problematic as far as grapefruit juice goes. To be on the safer side, patients are often advised to avoid grapefruit and grapefruit juice entirely while taking statins, Qato says.

Grapefruit can cause problems when mixed with other medications, too. A few include some antianxiety drugs, such as BuSpar, and certain corticosteroids that treat Crohn’s disease or ulcerative colitis, such as Entocort EC and Uceris tablet (both budesonide), according to the U.S. Food and Drug Administration.

5. Bananas and other potassium-rich foods, plus ACE inhibitors

If you take blood pressure-lowering ACE inhibitors with potassium-rich foods, including bananas, avocados, tomatoes and dried apricots, you can get high potassium levels in your body, which can lead to potentially dangerous heart arrhythmias, Brown warns. That’s why it’s wise to limit your intake of potassium-rich foods while taking an ACE inhibitor. It’s recommended that some ACE inhibitors, such as captopril and moexipril (brand names Capoten and Univasc), be taken at least an hour before meals.   

6. Fruit juice and some blood pressure drugs/ antihistamines

If you’re taking a calcium channel blocker (another type of hypertension drug), steer clear of grapefruit juice because it can render the drug ineffective, Qato says. Also, if you’re taking the beta blocker atenolol (Tenormin) or the renin inhibitor aliskiren (Tekturna), you should know that drinking apple juice or orange juice could decrease levels of the drug in your body.  ​

In a lesser-known interaction, some of the newer generation of antihistamines — namely, fexofenadine (Allegra) — can also interact with acidic juices, such as apple juice, orange juice and grapefruit juice, Qato says. “These acidic juices could affect absorption and neutralize the effect of antihistamines so they don’t really work.” If you’re seeking allergy relief, Qato advises avoiding these juices within two to four hours of taking one of these antihistamines.

7. High-fiber foods and levothyroxine, digoxin

Consuming soybean flour, walnuts and other high-fiber foods can make levothyroxine — a drug listed under several brand names that is used to treat an underactive thyroid gland — less effective. The same is true if you’re taking digoxin, which is sold under several brand names and is used to treat heart failure. High-fiber foods can affect a person’s absorption of the drug, Qato explains, so your best bet is to take digoxin at least two hours before or after consuming meals or snacks that are loaded with fiber.