What Are the 10 Most Common Drugs to Interact with Foods?

Savannah Helm

By: Eric Christianson, PharmD, BCPS, BCGP with Madison Bonn, PharmD Candidate, and Alicia Jerome MS, RDN

Dr. Eric Christianson, states, “I’d encourage every RDN to have a go-to pharmacist within their organization or community. There are so many medication problems to solve, and you will be asked medication questions when working with patients. I’d encourage you not to “wing-it” on medications and use a pharmacist’s expertise to your advantage.”  

  1. MAOIs and tyramine containing foods - Some monoamine oxidase inhibitors (MAOIs) and foods containing high levels of tyramine can cause a hypertensive crisis. The MAOIs block the monoamine oxidase enzyme that breaks down tyramine. Watch out for foods that are fermented, cured, pickled, aged, or spoiled. Such as aged cheese, meats, soy products, and yeast products. Fortunately, MAOIs aren’t frequently used in clinical practice but you shouldn’t be caught off guard by this risk if you see one. 
  2. Vitamin K and Warfarin - Foods containing Vitamin K decrease the effectiveness of Warfarin resulting in the patient being at an increased risk for clotting. Vitamin K is needed to make proteins for blood clotting. Warfarin inhibits the vitamin K epoxide reductase complex 1 (VKORC1) which inhibits Vitamin K from creating clotting factors. Patients should not exclude Vitamin K-containing foods from their diet like dark green vegetables, but rather maintain a consistent intake of Vitamin K daily. This is because the dose of the medication is adjusted to counteract their everyday consumption of the vitamin. If there is ever a diet change reported, checking an international normalized ratio (INR), or the test used to measure the effectiveness of an anticoagulant medication can help ensure that warfarin use is appropriately monitored.
  3. Grapefruit and statins - Grapefruit or grapefruit juice can increase the concentrations of some statins. Grapefruit inhibits CYP3A4, an enzyme in the intestines that breaks down statins and reduces the amount entering the bloodstream. Patients and healthcare professionals often have misconceptions about this interaction. (Read Dr. Christianson’s blog post on this misconception or listen to his recent podcast episode on grapefruit juice.) 
  4. Grapefruit and calcium channel blockers - Calcium channel blockers (CCB) like verapamil, diltiazem, and amlodipine can interact the same way that grapefruit interacts as with statins. Drug concentrations of the calcium channel blocker may rise, increasing the risk of adverse effects like edema, constipation, and hypotension.
  5.  Dairy calcium and tetracyclines - The calcium in dairy products binds to a class of antibiotics called tetracyclines (doxycycline is most commonly used in this class) and inhibits the absorption of the medication in the gastrointestinal tract. Patients should wait two hours after ingesting dairy to take the antibiotic and then wait an hour after before taking dairy.
  6. Fiber and digoxin - Foods containing insoluble or soluble fiber can slow down the absorption of digoxin, an antiarrhythmic and blood pressure medicine, leading to lower concentrations and decreasing its effectiveness. This medication should not be taken with meals containing a lot of insoluble fiber.
  7. Alcohol and numerous drugs - Drinking alcohol increases the risk for entral nervous system (CNS) depression. This risk is exacerbated by numerous medications including opioids (oxycodone, morphine), benzodiazepines (lorazepam, clonazepam), and gabapentin. Higher doses of these medications and larger intake of alcohol will escalate this risk. 
  8. Vitamin C and ADHD drugs - Foods that have a large amount of vitamin C will prevent absorption of ADHD medications such as Adderall and Ritalin. Citrus juices, soda, and foods with a large amount of vitamin C should be avoided an hour before taking the medication. Clinical monitoring is important when patients have a change in their dietary intake of vitamin C.
  9. Caffeine and Ciprofloxacin - Ingesting caffeine while on Ciprofloxacin can increase the levels of caffeine. Caffeine is mainly converted to paraxanthine by CYP1A2 before getting eliminated from the body. Ciprofloxacin inhibits CYP1A2 and slows down this conversion causing the half-life (and drug concentrations) of caffeine to increase. This may lead to caffeine side effects of anxiety, insomnia, and heart-pounding.
  10.  Sodium and lithium - Salt intake may affect concentrations of lithium. A sudden decrease in sodium results in higher serum lithium levels and vice versa. Lithium does not get metabolized in the body and is almost entirely eliminated by the kidneys. Anything that affects renal function will change the rate of elimination. This includes age, dehydration, and sodium balance.

Dr. Eric Christianson, a consultant pharmacist based in Minnesota, has made it his life’s work to provide medication safety education through his website MedEd101.com and through his podcast Real Life Pharmacology. Helm Publishing currently offers a 15 and 25 CPE course on his book: MedEd101 Guide to Drug and Food Interactions.


  1. Christianson, E., & Salling, J. (2020). MEDED101 Guide to Drug Food Interactions. CreateSpace Independent Publishing Platform.
  2. S. Department of Health and Human Services. (2014). Harmful interactions. National Institute on Alcohol Abuse and Alcoholism. Retrieved October 20, 2021, from https://www.niaaa.nih.gov/publications/brochures-and-fact-sheets/harmful-interactions-mixing-alcohol-with-medicines.


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