Key takeaways

Grapefruit juice can increase the side effects of certain medications, including prescription statins and over-the-counter drugs like certain antihistamines, affecting their breakdown in the liver and intestines.
Dairy products can reduce the effectiveness of certain antibiotics, such as ciprofloxacin, levofloxacin, and doxycycline, by decreasing their bioavailability (and making them less effective) when consumed together.
High-potassium foods, such as bananas, can lead to an excessive buildup of potassium in the body when taken with ACE inhibitors, causing significant heart rhythm problems.
Alcohol can amplify side effects such as nausea and dizziness when mixed with medications, and can also reduce the effectiveness or cause toxicity of certain drugs. Combining alcohol with certain medications, such as benzodiazepines for anxiety or opioids for pain, can result in slow and shallow breathing (respiratory depression), which can cause death.

If you’ve ever taken the wrong medication on an empty stomach, you know the importance of reading the outside of your pill bottle. It’s not uncommon for the pharmacy to warn you not to take certain drugs with a meal. But did you know that what you eat can affect your medication?

What are food-medication interactions?

According to the FDA, food and medication interactions occur as a result of medications reacting with certain beverages or foods. Alcohol, for example, can make you feel drowsy when mixed with some drugs. Research indicates that some food-drug interactions can lessen a drug’s effects or increase its side effects. That’s why it’s important to speak with your provider or pharmacist about possible interactions any time you begin a new medication.

7 common food-drug interactions

Food and drug interactions can make prescription drugs and over-the-counter medications less effective or cause dangerous side effects. If you find out that a medication you are taking has a food interaction, it may be enough to avoid eating the food for one to two hours before and after taking the medication. But other times, you may need to avoid a specific food altogether. It’s always best to reach out to your healthcare provider for guidance on food and medication interactions. Here are a few common culprits.

1. Grapefruit juice

Are you on a prescription statin, like Lipitor or Zocor? Then you might want to lay off the grapefruit juice. Compounds from the fruit (called furanocoumarins) can actually prevent an enzyme in your liver and intestines from breaking down the medicine. This can lead to a higher concentration of the drug in the body and potentially result in increased side effects.

But even if you aren’t on a statin, you might want to beware of grapefruit-drug interactions. “What people don’t realize is that it can interact with a large number of drugs, not just statins,” says Morton Tavel, MD, author of Health Tips, Myths and Tricks: A Physician’s Advice. “Anyone taking virtually any medication should avoid grapefruit juice entirely.” This includes over-the-counter antihistamines, calcium channel blockers, birth control, and others.

RELATED: Grapefruit and statins

2. Dairy

If you’re on a course of antibiotics, don’t wash your pills down with a glass of milk. Dairy products can make certain antibiotics, including ciprofloxacin, levofloxacin, and doxycycline, less effective.

“If you have milk products in your stomach, those drugs become a lot less bioavailable,” says Dr. Len Horovitz, an internist at Lenox Hill Hospital.

People on monoamine oxidase inhibitors (MAOIs) should also cut back on strong, aged cheeses, such as Parmesan and Camembert. These cheeses have high levels of tyramine, an amino acid that helps keep your blood pressure in check. High levels of tyramine are associated with migraine headaches and high blood pressure.

“MAOIs block the enzyme responsible for breaking down tyramine, which can cause it to build up and raise your blood pressure,” Dr. Tavel says.

3. Bananas and other potassium-rich foods

A high concentration of potassium makes bananas healthy for most of us. But you could end up with too much potassium if you eat a bunch of bananas while taking an angiotensin converting enzyme (ACE) inhibitor, like lisinopril or captopril. These medications can cause the body to retain excess potassium that would otherwise be flushed out by the kidneys.

“Potassium is a great mineral and necessary in our diets, but under certain circumstances it can lead to trouble,” Dr. Tavel says. “An excessive build-up of potassium can lead to significant problems with your heart rhythm.”

While bananas are the best-known food for potassium, they’re far from the only food with an abundance of the mineral. Limit your intake of sweet potatoes, mushrooms, potatoes and other high-potassium foods when taking ACE inhibitors. Additionally, salt substitutes often replace sodium with potassium chloride.

RELATED: Does potassium affect your blood pressure?

4. Black licorice

Black licorice is a polarizing candy. If you happen to love it, you might need to switch to red Twizzlers if your doctor writes you a prescription for digoxin, Dr. Tavel advises. Black licorice contains a compound called glycyrrhizin, which can lower potassium levels and cause a toxic effect from digoxin.

And even if you stop taking the medication, you might consider giving up black licorice for good. The FDA has warned that just two ounces of black licorice a day for two weeks can give people 40 years of age and older an irregular heartbeat, requiring hospitalization.

5. Green leafy vegetables

Green vegetables including broccoli, cabbage and Brussels sprouts, along with leafy greens, such as spinach and kale, are rich in nutrients, including vitamin K. Vitamin K plays a key role in helping blood to clot, thus preventing excessive bleeding. However, it actually counteracts the effects of a common blood thinner called Coumadin (also known by its generic name, warfarin).

If you are prescribed warfarin, your doctor will recommend that you don’t drastically alter your intake of foods high in vitamin K. Eating more green leafy vegetables than you normally do can decrease the effects of blood thinners like warfarin and increase the risk of adverse events like heart attack and stroke.

6. Alcohol

Alcohol can be harmful if taken with many medications. Mixing alcohol with medications can amplify certain side effects, such as nausea, vomiting, headaches, fainting, or loss of coordination. Alcohol has also been known to make medications less effective or possibly toxic to the human body.

Drinking alcohol with anti-anxiety medications like benzodiazepines can cause increased drowsiness or dizziness. The combination of alcohol and opioid painkillers has a similar effect and can even lead to slow and shallow breathing (respiratory depression), which can be fatal. Alcohol should also be avoided with products containing acetaminophen due to an increased risk of liver damage. Additionally, drinking while taking insulin and other oral diabetes medications can cause low blood sugar. Overall, it’s best to avoid alcohol use with certain medications.

7. Fiber

High fiber meals and dietary supplements containing fiber may reduce the effectiveness of some medications. These include statins like simvastatin, ezetimibe, pravastatin and fluvastatin, tricyclic antidepressants such as Elavil (amitriptyline), Sinequan (doxepin), and Tofranil (iImipramine), and the mood stabilizer Lithium. Fiber and fiber supplements can also reduce the effectiveness of other medications, including the diabetes drugs Diabeta (glyburide) Metformin (glucophage), the seizure medication Tegretol (carbamazepine), and the heart medication Lanoxin (digoxin).

To avoid reduced or delayed absorption of your medication, take it one hour before or two to four hours after consuming fiber or taking a fiber supplement.

How to check for food-drug interactions

These foods are simply seven of hundreds of potential food-drug interactions. Ask your pharmacist about foods you should avoid next time you pick up your prescription.

If a drug has food interactions, warnings will be noted on the medication’s label or package insert, so be sure to read the information thoroughly. It’s also important to discuss possible food-drug interactions with your prescribing physician so that you can determine which foods to avoid or eat with medication.