Services at Banner – University Medical Center Phoenix  

Understanding Food and Drug Interactions


Banner Family Pharmacy wants to help you learn more about food-drug interactions.

What Is a Food-Drug Interaction?
Any time that a food or beverage changes the effects of a drug, the change is considered a food-drug interaction. Food-drug interactions can occur with prescription drugs, over-the-counter drugs, herbal products, and dietary supplements.

What Are Some Common Food-Drug Interactions?

  • Tyramine and MAO inhibitors: Foods that contain the substance tyramine (including beer, wine, avocados, some cheeses, and some processed meats) slow down enzymes that metabolize MAO inhibitors (a type of antidepressant medication) and can cause dangerously high blood pressure.
  • Calcium and antibiotics: if you drink a glass of milk when taking the prescription antibiotic tetracycline, the calcium in the milk will bind to the tetracycline, making a compound that is impossible for your body to absorb. Therefore, the desired effect of the tetracycline (as well as the benefits of calcium) will not occur.
  • Vitamin C and iron: Drinking a glass of citrus juice at the same time that you take an iron supplement is beneficial because the vitamin C in the citrus juice increases the absorption of iron.
  • Warfarin and vegetables: People who use the blood-thinning drug warfarin should eat a consistent amount of foods such as broccoli or spinach because vitamin K helps make blood clot, therefore reversing the effect of warfarin.
    The opposite can happen with vitamin E, onions, and garlic because they all can cause blood-thinning. Large amounts of these foods can make the effects of warfarin too powerful.

The Most Commonly Misunderstood Interaction: Grapefruit Juice
The fact is that although some medications may interact with grapefruit juice, most do not. Also, it is believed to be safe to consume grapefruit juice while taking any over-the-counter medication.  
If you are concerned, ask your doctor or pharmacist if your medication interacts with grapefruit juice.

What If I’m Not Supposed to Eat a Food I Love?
If your doctor or pharmacist advises you to avoid certain foods while taking a medication, it is very important to avoid that food but other options may be available.

Some food-drug interactions occur only if the food is eaten at the same time that you take your medication.  Your doctor may be able to switch you to another drug that has similar effects but will not interact with the food

How Do I Know If a Certain Food Is Safe to Eat?
Luckily, the number of food-drug interactions with harmful results is small but there are some steps to take to be careful:

  • Read the labels of all prescription and over-the-counter drugs to check for interactions.
  • Talk with your doctor or pharmacist about any known food (or drug) interactions with your medications and clarify treatment options.
  • If your medications do not seem to produce the desired effects, or if you experience unwanted side effects, review your diet with your doctor or pharmacist to assess for food-drug interactions.


Banner – University Medical Center Phoenix
1111 E. McDowell Road
Phoenix, AZ 85006
(602) 839-2000
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