Food and Drug Interaction Safety Guide

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

Levothyroxine, a common thyroid medication, also interacts with the calcium in milk, calcium supplements and calcium-fortified foods, according to research. The U.S. Food and Drug Administration (FDA) recommends taking levothyroxine on an empty stomach and waiting 30 to 60 minutes before eating breakfast.  

2. Leafy greens and warfarin

Another potential food-drug interaction 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 reduce the risk of 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, since a consistent intake is the best strategy for most patients. For example, the American Heart Association now says most people taking warfarin can consume foods high in vitamin K, as long as they keep their vitamin K intake consistent, and avoid large amounts at once. “If you like salad, have it three times a week and the same amount each time,” Brown advises, so your warfarin concentration stays 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. The drugs reduce your body’s ability to metabolize tyramine, leading to a high tyramine level that can trigger a sudden, dangerous increase in blood pressure. Foods that are high in tyramine include smoked and cured meats, pickled or fermented foods, red wine, some draft beer, soy products (soy sauce, miso, tofu), very ripe bananas, and strong or aged cheeses, including aged cheddar, Swiss and Parmesan. Newer research suggests tyramine levels in many foods are lower than they once were, but experts still recommend avoiding foods known to be high in tyramine while taking an MAOI.

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. 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 cholesterol-lowering 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. The risk of a significant interaction increases with higher amounts of grapefruit juice. The FDA recommends avoiding large quantities (defined as more than one quart per day). To be on the safe 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. Among them: some drugs that treat anxiety (buspirone), high blood pressure (nifedipine), abnormal heart rhythms (amiodarone) and corticosteroids that treat Crohn’s disease and ulcerative colitis (budesonide as Entocort EC and Uceris tablet), according to the FDA.

A 2020 study suggests juice from pomelo and Seville (sour) oranges may also interact with certain drugs, but the evidence is far less extensive. And although some experts have expressed concerns about cranberry and pineapple juice interactions, the review found that the evidence has been inconclusive.

5. Bananas and other potassium-rich foods, plus certain blood-pressure medications

If you take an angiotensin converting enzyme (ACE) inhibitor or angiotensin II receptor blockers (ARBs) for your heart or blood pressure, potassium-rich foods can cause your potassium levels to skyrocket, leading to potentially dangerous heart arrhythmias, Brown warns. That’s why it’s wise to limit your intake of potassium-rich foods such as bananas, avocados, tomatoes and dried apricots. Also, be wary of potassium supplements and salt substitutes that contain potassium. Some ACE inhibitors, such as captopril and moexipril (brand name Univasc), should be taken at least an hour before meals.

6. Fruit juice and some blood pressure drugs/ antihistamines

If you’re taking certain calcium channel blockers for high blood pressure, ask your doctor if you should steer clear of grapefruit juice because it could cause side effects. 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 newer antihistamines — namely, fexofenadine (Allegra) — can also interact with acidic juices, such as apple, orange 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 for two to four hours after taking one of these antihistamines.

7. High-fiber foods and levothyroxine, digoxin

Consuming whole-wheat bread, bran, psyllium and other high-fiber foods can make levothyroxine — a drug listed under several brand names and used to treat an underactive thyroid gland — less effective, according to a 2021 systematic review published in the journal Pharmaceuticals.

The same is true if you’re taking digoxin, which is sold under several brand names and is used to treat heart failure and chronic atrial fibrillation. High-fiber foods can affect a person’s absorption of the drug, Qato explains. Take levothyroxine at least one to one and a half-hour before or after food, and digoxin at least two hours before or after consuming meals or snacks high in fiber.

8. Licorice and blood pressure medications

Black licorice may taste sweet, but the candy can have some pretty sour health effects. The confection contains the compound glycyrrhizin, which can trigger abnormal heart rhythms and high blood pressure in some people. In fact, the FDA issued a warning a few years back saying that if you’re older than 40, eating 2 ounces of black licorice a day for at least two weeks could land you in the hospital with an irregular heart rhythm or arrhythmia.

Licorice can also interact with medications and supplements, the FDA says, including those prescribed for high blood pressure. People taking these medications should not use licorice products, health experts say, as it can make side effects worse or cause potassium to build up in the body.

Licorice can also interact with MAOI inhibitors, blood thinners and medications processed by the liver.

What medications should be taken with no food?

Many medications work best when taken on an empty stomach, because food can make it harder for your body to absorb their active ingredients. Examples include the thyroid medication levothyroxine, osteoporosis drugs, as well as some antibiotics and blood pressure medications.

Unless the label says otherwise, taking on an empty stomach usually means at least one hour before eating or two hours after. Because directions vary by drug, it’s important to check the label or ask your doctor or pharmacist for guidance.

Beware of fortified foods

In an often-overlooked phenomenon, certain medications can interact with the vitamins and minerals that are added to everyday foods like breakfast cereal, bread and milk — especially calcium, iron, magnesium and zinc.

And while “the prescription label may warn you not to take the drug with calcium or iron, it doesn’t mention fortified foods,” where these nutrients often hide, Brown says.

The trouble is, if you have an infection and take an antibiotic like tetracycline, doxycycline or ciprofloxacin along with calcium-fortified orange juice or a super-fortified energy bar, cereal or smoothie, the minerals may bind with the drug and inhibit its absorption in the body, Brown explains. This increases the chances that the treatment could fail or be insufficient to produce optimal results. And if you consume multiple fortified foods in the same meal, this could have a pronounced effect on your body’s ability to absorb the medication.

The best ways to protect yourself from this risk: If a drug’s package insert warns you not to take the medication with calcium supplements, antacids, iron-containing supplements or dairy products, “that’s a red flag that there could be an interaction with fortified foods that contain the same nutrients,” Brown says.

It’s also wise to ask your pharmacist or doctor if you should avoid certain nutrients close to the time that you take the medicine. To be on the safe side, take the drug an hour or two before having calcium-fortified juice, a fortified cereal or a nutrient-dense energy bar or drink — or to wait three hours after having the food or beverage to swallow the drug. That way, “your body will have enough time to absorb the medication,” Brown says.

Don’t forget about alcohol

Numerous classes of drugs — from antibiotics to pain medications, even over-the-counter pills — can interact with alcohol and cause side effects that range from unpleasant to downright dangerous. Be sure to check with your doctor or pharmacist before drinking alcohol when taking medications.