Food and medicine interactions to know
Some foods change how medicines work — making them stronger, weaker, or riskier. Here are the best-documented ones, in plain language, each checked against FDA, NIH or MedlinePlus guidance.
This guide helps you know what to ask. Your doctor or pharmacist can tell you whether an interaction applies to your exact medicine and dose.
Grapefruit and many common medicines
Grapefruit can change how much of some medicines reaches your blood.
- Foods involved
- Grapefruit, grapefruit juice, Seville oranges, pomelos, tangelos
- Medicines involved
- Some statins (such as simvastatin and atorvastatin), some blood-pressure medicines (such as nifedipine), and others including cyclosporine, buspirone, budesonide, amiodarone and fexofenadine.
- What happens
- For most affected medicines, grapefruit blocks an enzyme in the gut (CYP3A4) that normally breaks the drug down, so more of it enters the blood and side effects become more likely. For fexofenadine (Allegra) it works the other way: less drug is absorbed. How strong the effect is depends on the person, the medicine and how much juice.
- What to do
- Check your medicine's leaflet or label and ask your pharmacist whether grapefruit — and related citrus — is safe for you.
Source: FDA: Grapefruit Juice and Some Drugs Don't Mix · MedlinePlus: Atorvastatin
Vitamin K foods and warfarin
Keep vitamin K intake steady if you take warfarin.
- Foods involved
- Kale, Spinach, Broccoli, Brussels Sprouts, Parsley, other leafy greens, some vegetable oils
- Medicines involved
- Warfarin (Coumadin, Jantoven).
- What happens
- Vitamin K helps blood clot, and warfarin works by opposing it. Sudden changes matter: eating much less vitamin K can raise bleeding risk, and eating much more can make warfarin less effective and raise clot risk.
- What to do
- You don't need to avoid greens. Aim for about the same amount week to week, and tell your care team before big diet changes or starting supplements.
Source: MedlinePlus: Warfarin · NIH Office of Dietary Supplements: Vitamin K
Potassium and some blood-pressure medicines
Some medicines raise blood potassium; salt substitutes can add more.
- Foods involved
- Potassium-based salt substitutes, Bananas, Oranges, Avocado, Tomatoes, cooked Spinach, Asparagus, dried fruit such as Dates
- Medicines involved
- ACE inhibitors (such as lisinopril), angiotensin receptor blockers (ARBs), and spironolactone. Kidney disease raises the risk too.
- What happens
- These medicines can make the body hold on to potassium. Too much potassium in the blood can affect heart rhythm. Salt substitutes are often potassium chloride, which adds up quickly.
- What to do
- Talk to your doctor before using salt substitutes or potassium supplements. If you've been told to watch potassium, ask how much high-potassium food fits your plan.
Source: MedlinePlus: Lisinopril · MedlinePlus: High potassium level
Dairy, calcium and certain antibiotics
Calcium can bind some antibiotics and stop them working well.
- Foods involved
- Milk, Greek Yogurt, Cottage Cheese, cheese, Ice Cream, calcium-fortified juice
- Medicines involved
- Tetracycline antibiotics and ciprofloxacin. Calcium, iron and antacid supplements also matter for these drugs and for levothyroxine.
- What happens
- Calcium (and iron, magnesium and zinc) can bind to these antibiotics in the gut so less is absorbed.
- What to do
- Tetracycline is taken away from food, especially dairy. Ciprofloxacin shouldn't be taken with dairy or fortified juice alone, though a meal containing them is OK. Follow the timing on your prescription label.
Source: MedlinePlus: Tetracycline · MedlinePlus: Ciprofloxacin
Levothyroxine (thyroid hormone) and food
Some foods can reduce how well levothyroxine is absorbed.
- Foods involved
- Soy foods such as Tofu and Edamame, Walnuts, high-fiber foods, Grapefruit
- Medicines involved
- Levothyroxine (Synthroid, Levoxyl and others).
- What happens
- Levothyroxine is usually taken on an empty stomach, 30–60 minutes before breakfast, because food can interfere with absorption. Calcium and iron supplements need to be taken hours apart.
- What to do
- Take it the same way every day and ask your doctor before making big changes to soy, walnut or fiber intake.
Source: MedlinePlus: Levothyroxine
Tyramine foods and MAOI antidepressants
Aged, smoked or fermented foods can cause a dangerous reaction with MAOIs.
- Foods involved
- Aged or smoked cheeses, smoked, aged or spoiled meats and fish (such as some cured meats), fermented yeast products, alcoholic drinks
- Medicines involved
- Monoamine oxidase inhibitors (MAOIs) such as phenelzine. Caffeine should be avoided as well.
- What happens
- Eating foods high in tyramine while taking an MAOI can cause a serious reaction.
- What to do
- If you take an MAOI, get a written food list from your doctor or dietitian and follow it closely.
Caffeine and medicines
Some medicines make caffeine's effects stronger.
- Foods involved
- Coffee, Green Tea, cola and energy drinks, Dark Chocolate
- Medicines involved
- Ciprofloxacin can increase caffeine's jitteriness, sleeplessness and racing heart. MAOIs require avoiding caffeine. Other medicines can make people more sensitive to it.
- What happens
- For most healthy adults the FDA cites up to about 400 mg of caffeine a day — roughly two to three 12-oz cups of coffee — as not generally linked to negative effects.
- What to do
- If you're pregnant, breastfeeding or on medication, ask your clinician how much caffeine is right for you.
Source: FDA: Spilling the Beans — How Much Caffeine Is Too Much? · MedlinePlus: Ciprofloxacin
Alcohol and common medicines
Alcohol can raise the risk of side effects from several everyday medicines.
- Foods involved
- Beer, wine and spirits
- Medicines involved
- Metformin (raises the risk of lactic acidosis and low blood sugar), atorvastatin (higher risk of serious side effects), MAOIs, and warfarin.
- What happens
- Alcohol is processed by the liver alongside many medicines and can add to their side effects.
- What to do
- Tell your doctor how much you drink and ask what is safe with your medicines.
Source: MedlinePlus: Metformin · MedlinePlus: Atorvastatin · MedlinePlus: Warfarin
Cranberry and warfarin
Evidence on a cranberry–warfarin interaction is conflicting.
- Foods involved
- Cranberries, cranberry juice and supplements
- Medicines involved
- Warfarin.
- What happens
- Studies disagree on whether cranberry changes warfarin's effect. Separately, cranberry may modestly lower the risk of repeat urinary tract infections in some women, but it is not a treatment for an existing UTI.
- What to do
- If you take warfarin, check with your care team before using cranberry products regularly.
Source: NCCIH: Cranberry
Tips for any medicine
- Read the leaflet or label that comes with your medicine — food warnings are listed there.
- Keep an up-to-date list of everything you take, including supplements and herbal products, and share it at every appointment.
- Ask your pharmacist: “Is there any food or drink I should avoid or time differently with this?”
Last reviewed October 2026.
General information only, not medical advice. If you take medicine or manage a health condition, check with your doctor, pharmacist or a registered dietitian before changing your diet. Read our medical disclaimer.