If you’ve ever been told not to eat a specific food while taking a medication, it was likely due to the possibility of a medication interaction.
Some medications work less effectively or cause unpleasant side effects when mixed with certain foods, beverages, vitamins, or supplements. (As you’ll learn below, sometimes taking a medication as prescribed means avoiding grapefruits.)
Several factors affect how a medication works, and interactions can happen between:
Two or more medications
A medication and a food or beverage
A medication and vitamins or supplements
A medication and a health condition
Most potential medication interactions are known. So as long as your provider is aware of your health history and all the medications you’re currently taking — including over-the-counter ones — you should be able to experience the benefits of your medications and avoid unnecessary side effects.
It’s also helpful to understand why these interactions occur. Below, you’ll find an overview of medication interaction basics. In addition, always ask your doctor or pharmacist as many questions as you need to in order to feel confident taking your medications.
What causes medication interactions?
Proteins in your liver called enzymes are responsible for helping your body absorb and process a medication. Sometimes a medication, vitamin, or supplement changes how these enzymes work.
If one medication causes enzymes to break down another medication more slowly, you may experience an interaction between the two medications. This can cause a medication to stay in your body for too long, or increase its quantity in your body. Both scenarios can lead to unwanted side effects or worsen side effects that you typically experience.
On the flip side, a medication interaction might cause enzymes to work faster, making medication pass through your body too quickly. In these types of medication interactions, you won’t experience a medication’s normal benefits, which can worsen symptoms of a health condition.
Other times, a food or supplement binds to an oral medication, preventing that medication from entering your bloodstream or lowering your blood levels of it.
Keep in mind that each person’s body and genetic makeup is unique. Your specific genes can profoundly impact how medications are metabolized and any resulting medication interactions.
Interactions between two medications
A medication-medication interaction occurs when the combination of two or more medications produces an unwanted side effect. As an example, when the heart medication digoxin (Lanoxin®) is combined with another heart medication called amiodarone (Pacerone®), blood levels of digoxin may increase, resulting in side effects.
Other examples of medication-medication interactions include:
Anticoagulants and antibiotics/OTC pain relief: Antibiotics and many common pain relief medications including ibuprofen (Advil®, Motrin®) and naproxen (Aleve®) aren’t safe to combine with blood-thinning medications like warfarin (Coumadin®, Jantoven®), as they can increase the risk of bleeding.
Levothyroxine and omeprazole: The thyroid medication levothyroxine (Synthroid®) requires extremely precise dosing and other medications can easily alter blood levels of it. In particular, the heartburn medication omeprazole (Prilosec®) can decrease the body’s absorption of levothyroxine.
Diuretics and certain antidepressants: Diuretics, a class of blood pressure-lowering medications that includes chlorthalidone (Thalitone®, Tenoretic®, and Clorpres®) and hydrochlorothiazide (HydroDiuril®, Microzide®, and Esidrix®), can lower sodium levels. Combining these medications with certain antidepressants including fluoxetine (Prozac®) and venlafaxine (Effexor XR®) can increase the risk of severely low sodium levels.
Interactions between medication and food
Even some of the most nutritious foods can pose health risks when combined with certain medications. For example, grapefruits and grapefruit juice can block the enzymes your body needs to break down cholesterol-lowering statins, leading to higher blood levels of the medication and a greater risk of side effects.
Some statins interact more strongly with grapefruits and grapefruit juice — like atorvastatin (Lipitor®), lovastatin (Mevacor®, and simvastatin (Zocor®) — while others, including fluvastatin (Lescol®) and pravastatin (Pravachol®), are less affected. If you have concerns about this potential medication interaction, speak with your doctor about your options.
Other common food-medication interactions include:
Warfarin and vitamin K-rich vegetables: The anticoagulant warfarin blocks the effects of vitamin K, which helps your blood clot. High intake of vitamin K-rich veggies like broccoli and spinach can make the medication less effective. Consult with your doctor about nutrition considerations when taking warfarin, and maintain a consistent diet.
Metformin and alcohol: Drinking heavily while taking the oral diabetes medication metformin can increase your risk of extremely low blood sugar. In rare cases, it can also cause a condition called lactic acidosis, in which too much acid accumulates in the bloodstream. Many people are able to safely drink in moderation while on metformin. The specific interaction of alcohol and metformin varies by individual. Consult with your doctor to determine what precautions you should take.
Dairy products and antibiotics: Milk, yogurt, cheese, and other dairy products can reduce the body’s absorption of certain antibiotics, including tetracycline, doxycycline, ciprofloxacin, and minocycline.
Dairy products and bisphosphonates: Dairy products can also reduce absorption of some oral bisphosphonates used to treat osteoporosis.
As a precaution against food-medication interactions, ask your doctor or pharmacist about the best ways to take your medication. The potential for these interactions doesn’t necessarily mean avoiding certain food or drinks altogether, but rather making small modifications or being mindful of when you eat or drink them. For example, it is typically recommended to consume dairy products at least three hours after taking an antibiotic.
Interactions between medication and a health condition
Doctors need to know your health history in order to safely prescribe a medication. Certain health conditions may increase a medication’s side effects, and some medications can worsen symptoms of a health condition.
Examples of interactions between a medication and health condition include the following. If you are concerned about the possibility of a medication-condition interaction, speak with your doctor about appropriate alternative medications.
Decongestants and hypertension: Some decongestants used to relieve colds, including pseudoephedrine (Sudafed®), can tighten blood vessels throughout your body, increasing blood pressure. If you have high blood pressure, look for decongestant-free cold medicines like Coricidin®.
Nonsteroidal anti-inflammatory drugs (NSAIDs) and hypertension: Nonsteroidal anti-inflammatory drugs (NSAIDs) including ibuprofen and naproxen can also increase blood pressure. Aspirin or acetaminophen (Tylenol®) is typically a better option for pain or fever relief for individuals with hypertension.
Beta blockers and asthma: Beta blockers, a medication class commonly used to lower blood pressure, can tighten airway muscles, potentially causing an asthma attack.
Acetaminophen and liver function issues: Your liver is critical in your body’s absorption of acetaminophen. If your liver function is impaired, the medication can accumulate in your bloodstream and further damage your liver. If you have any known issues with liver function, ask your doctor if acetaminophen is safe to take. They may recommend a lower dosage or suggest taking an alternative medication.
Avoiding harmful medication interactions
The best way to prevent any negative medication interaction is to make sure that anyone prescribing a medication for you is informed of your entire health history. This is especially important if you see multiple doctors, take multiple medications, or live with a chronic health condition.
When you are prescribed a medication, speak with your doctor or pharmacist about all the medications you take — both OTC and prescription — as well as supplements, vitamins, and herbs. They should also have a sense of your diet.
Consolidating your prescriptions at one pharmacy can also prevent interactions between multiple medications. At Alto, we check for potential interactions when we receive a new prescription by reviewing every prescription on file.
You should always know the answers to the following questions when taking a medication. Never hesitate to ask your doctor or pharmacist for additional clarification.
Can I take this medication with other medications?
Should I avoid certain foods or drinks when taking this medication?
Are there known potential medication interactions? If so, what signs should I watch for?
The pharmacy care you deserve
Our expert pharmacists can answer any questions you have about medication interactions, side effects, or release right in the Alto app. We also offer free same-day delivery and medication management tools like reminders and auto refills to make it as simple as possible to stay on track with your treatment.
Reach out any time through secure in-app messaging or by phone at 1-800-874-5881.
This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition.
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