by Hellwig J

Drug Interactions: What You Need to Know

IMAGE You might know that certain prescription medications can interact with one another and cause potentially harmful side effects. But did you know that interactions can occur not only with prescription medications, but also with over-the-counter medications, supplements, and foods and beverages? Medications can even interact with diseases or conditions you may have. Fortunately, with a little careful planning, you can avoid serious drug interactions.

Types of Drug Interactions

There are 3 basic types of drug interactions:

Drug-Drug Interactions

These occur when one drug interferes with another drug, affecting how one or both act in or are eliminated from the body. These interactions can occur between prescription drugs, over-the-counter drugs, and even herbal or other dietary supplements, including vitamins. For example, vitamin E and aspirin both act to thin the blood. Taking these together could cause excessive bleeding. And combining antidepressants with the pain medication tramadol could cause seizures.
It is particularly important to remember that herbal products, which many people regard as natural alternatives to drugs, still behave like drugs in the body. For example, the herb called St. John’s wort can reduce blood levels of certain medications. Furthermore, if a person is already taking St. John’s wort along with another drug, stopping the herb may cause drug levels to rise, potentially leading to dangerous complications.

Drug-Food/Beverage Interactions

Drug-food/beverage interactions occur when a prescription or over-the-counter medication interacts with food or beverages. For example, taking the antibiotic tetracycline with a glass of milk can lessen the absorption of the antibiotic in the body and make it less effective. Grapefruit juice can block enzymes that metabolize numerous drugs, including some blood pressure-lowering drugs, anti-depressants, antihistamines, and the drug cyclosporine, thereby increasing blood levels of these drugs. Toxicity could result.

Drug-Condition Interactions

These occur when a prescription or over-the-counter medication interacts with a disease or condition. For example, decongestants, such as those found in many over-the-counter cold remedies, can cause an increase in blood pressure, which could be dangerous for people who already have high blood pressure.

Symptoms of Drug Interactions

The most common symptoms of drug interactions tend to be less serious and include the following:
  • Nausea
  • Headache
  • Heartburn
  • Lightheadedness
More serious—but less common—symptoms and results of drug interactions include the following:
  • Sharp increase or decrease in blood pressure
  • Irregular heartbeat
  • Buildup of toxins that could damage vital organs, such as the liver or heart
Consult your doctor or pharmacist if you experience any unusual side effect after taking a medication, no matter how mild or severe.

How to Avoid Drug Interactions

The key to avoiding drug interactions is to become informed about the potential interactions between all the drugs and dietary supplements you take by talking with your doctor and pharmacist.
Some steps you can take include:
  • Read the labels of all over-the-counter and prescription medications and dietary supplements carefully. Pay particular attention to the correct dosage and to the potential side effects and interactions associated with the drug or supplement.
  • Make sure you understand the benefits as well as the potential risks of any medication you are taking. Look specifically for the warning labels of over-the-counter medications.
  • Keep a record of all the medications and supplements you take, and share it with all the doctors and pharmacists involved in your care.
  • Talk to your doctor before taking any new medication or supplement.
  • Use one pharmacy for all your prescription medications.
  • Ask your pharmacist whether you should take a particular medication with food or on an empty stomach and if there are any foods or beverages that could interact with the drug.
  • Report any side effects you experience from any medications to your doctor or pharmacist.
  • Take medications only as directed and do not take any medications that were prescribed for someone else.
  • Purchase supplements and vitamins from a reputable source.
  • Look for a United States Pharmacopeia (USP) notation on the bottle of your supplement. USP is an organization that sets standards for prescription and OTC medications, healthcare products, food ingredients, and supplements.


United States Pharmacopeia (USP)
US Food and Drug Administration


Canadian Medical Association
Health Canada


Drug interactions: what you should know. US Food and Drug Administration website. Available at: Updated September 25, 2013. Accessed April 22, 2015.
Avoiding drug interactions. US Food and Drug Administration website. Available at: Updated November 28, 2008. Accessed April 22, 2015.
Mallet L, Spinewine A, Huang A. The challenge of managing drug interactions in elderly people. [review]. Lancet. 2007;370:185-191.
Neuvonen PJ. Interactions with the absorption of tetracyclines. Drugs. 1976;11(1):45-54.
Sansone R, Sansone L. Tramadol. Psychiatry. 2009 April;6(4):17-21. Available at: Accessed April 22, 2015.
Schardt D. St. John's worts and all. Nutrition Action Health Letter website. Available at: Accessed April 22, 2015.

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