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a pill with silverware Most of us have heard that certain medications, when taken together, can be potentially harmful. But what about food and medication? What possible harm could come from eating a cheese sandwich after taking an antibiotic? You may be surprised to learn that certain foods can dramatically affect your medications.

Knowing how and when to take your medications can eliminate or reduce interactions between food and drugs. Your pharmacist and your doctor can provide you with the most up-to-date information about these interactions.

Take this quick quiz to check your knowledge of food and drug interactions.

True or False?

Answer true or false for each of the following eight questions.

  1. Medication should always be taken with meals.
  2. Only prescription drugs interact with food.
  3. It is safe to take my medications with a glass of milk.
  4. I take high blood pressure medication. Therefore, I should use a potassium-containing salt substitute.
  5. Mineral oil is a harmless, gentle laxative.
  6. Any pharmacy can fill my prescriptions.
  7. Grapefruit juice is a harmless, healthy source of vitamin C.

How Did You Do?–The Answers

1. Medication should always be taken with meals—False The size and composition of a meal determines how quickly your medication will be absorbed. Some, such as aspirin and nonsteroidal anti-inflammatory medications (ibuprofen) irritate the stomach lining if you take them on an empty stomach. Others however, should be taken on an empty stomach. Food may slow their digestion or absorption. This is particularly true of some antibiotics.

2. Only prescription drugs interact with food—False Over-the-counter medications that you buy without a prescription, such as aspirin and low doses of ibuprofen, often interact with food. Watch out for alcohol, too. It blocks the effects of some drugs and intensifies the effects of others to dangerous levels. For example, alcohol combined with nitroglycerin can dangerously lower blood pressure. If you are taking antibiotic metronidazole, you may need to avoid alcohol completely.

3. It's safe to take my medications with a glass of milk—False Some drugs are negatively affected by dairy products. For example, the calcium in milk binds up tetracycline, a commonly prescribed antibiotic, so less tetracycline is absorbed. To prevent this, tetracycline should be taken at least two hours before or after eating dairy products or taking calcium supplements.

4. I take high blood pressure medication. Therefore, I should use a potassium-containing salt substitute—False This can sometimes be a dangerous misconception. Some blood pressure medications cause you to lose potassium, so your doctor may prescribe a potassium supplement. However, other classes of blood pressure medications actually prevent potassium loss. If you take potassium-sparing diuretics or ACE inhibitors, avoid liberal use of salt substitutes that contain potassium. Excessive use of these products causes an accumulation of potassium, which can lead to severe complications that can threaten your health or life.

5. Mineral oil is a harmless, gentle laxative—False Although gentle, mineral oil is a fat-soluble liquid. Mineral oil goes through the body undigested, robbing the body of fat-soluble vitamins like A, D, and E.

6. Any pharmacy can fill my prescriptions—True Any pharmacy can fill your prescriptions. However, it makes more sense to fill all your prescriptions at the same pharmacy. This enables the pharmacy's computer to keep track of all your medications so that the pharmacist can note any potential cross-reactions between existing medications and new ones. By visiting the same pharmacy all the time, you also create a relationship with the pharmacist. This makes you more likely to discuss any concerns you have.

7. Grapefruit juice is a harmless, healthy source of vitamin CFalse Grapefruit juice is healthy on its own, but it can interact with numerous medications, such as cholesterol lowering medications, potentially reducing their effects or increasing the risk of toxicity.

Other Food and Drug Issues

In addition to food and drug interactions, certain medications also affect taste, sensation, and appetite. For example, penicillin can make foods "taste funny." Antihistamines and certain antidepressants can cause dry mouth, making it hard to chew and swallow. Certain pain medications and iron supplements are a frequent cause of constipation.

How do you know when and how medications should be taken? Read the directions printed on the container and ask your doctor or pharmacist. Food and drug interactions are almost always avoidable or manageable.

To keep food-drug interactions at a minimum, follow these tips:

  • If you experience any unpleasant new symptoms after taking a new medication—or one you have been taking for a while—tell your doctor.
  • When a new medication is prescribed for you, tell your doctor and pharmacist about any other medications you routinely take, including herbal remedies, vitamin supplements, and nonprescription drugs.
  • Let your doctor know if you follow a special or restricted diet. Kosher diets have an unusually high sodium content, while traditional Asian diets may be high in both sodium and calcium. These factors may affect the types or even the brands of drugs prescribed for you.
  • Always take your medication at the time and in the manner prescribed. Taking too much or stopping too soon can be dangerous.
  • With each medical check-up, review your medications, lifestyle, and dietary habits. If you have recently lost weight or become a vegetarian, your medication doses may need to be changed.
  • FoodSafety.gov - US Department of Health and Human Services

    http://www.foodsafety.gov

  • US Food and Drug Administration

    http://www.fda.gov

  • Canadian Institutes of Health Research

    http://www.cihr-irsc.gc

  • Health Canada

    http://www.hc-sc.gc.ca

  • Antidepressant medication overview. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated April 25, 2014. Accessed May 9, 2014.

  • Antihypertensive medication management. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated March 17, 2014. Accessed May 9, 2014.

  • Avoid food-drug interactions. National Consumer League website. Available at: http://www.natlconsumersleague.org/health/146-food-drug-interactions/442-avoid-food-drug-interactions. Accessed May 9, 2014.

  • Drug interactions: what you should know. Center for Drug Evaluation and Research website. Available at: http://www.fda.gov/Drugs/ResourcesForYou/ucm163354.htm. Updated September 25, 2013. Accessed May 9, 2014.

  • Mineral oil. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated January 18, 2013. Accessed May 9, 2014.

  • Tetracycline. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated January 18, 2013. Accessed May 9, 2014.