Reducing Your Risk of Adverse Medication Interactions

Drug interactions occur when one drug interacts with another drug that you are taking or when your medications interact with what you eat or drink. Drug interactions can change the way your medications act in your body, making your medications less effective or causing unexpected and potentially dangerous side effects.

Your risk of having a drug interaction increases with the number of medications you use, both prescription and over-the-counter. Moreover, the type of medications you take, your age, diet, disease, and overall health can all affect your risk. Older adults are at greater risk for drug interactions than younger adults since a larger proportion of seniors take prescription medications or over-the-counter products. Here is a look at three important types of drug interactions.

Pill bottles on shelf
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Drug-Drug Interactions

Drug-drug interactions occur when two or more drugs interact with each other. Interactions can occur with prescription drugs, over-the-counter drugs, vitamins, and alternative medications such as supplements and herbal products. Some examples of drug-drug interactions include:

  • Mixing a prescription sedative to help you sleep with an over-the-counter antihistamine for allergies can cause daytime drowsiness and make driving or operating machinery dangerous.
  • Combining aspirin with a prescription blood thinner such as Plavix (clopidogrel) can cause excessive bleeding.
  • Some over-the-counter antacids interfere with the absorption of antibiotics into the bloodstream.
  • Certain medications used to treat fungal infections can cause serious side effects when combined with cholesterol-lowering medications such as Lipitor (atorvastatin).
  • Some herbal supplements, such as Ginkgo biloba, can cause bleeding if taken with aspirin.

Drug-Food Interactions

Drug-food interactions occur when a drug interacts with something you eat or drink. Some examples of drug-food interactions include:

  • Dairy products, such as milk, yogurt, and cheese, can interfere with the absorption of antibiotics into the bloodstream.
  • Many prescription drugs are affected by grapefruit juice. Grapefruit juice inhibits an enzyme in the intestine that normally breaks down certain drugs and hence allows more of a medication to enter the bloodstream.
  • Vegetables containing vitamin K, such as broccoli, kale, and spinach, can decrease the effectiveness of drugs, such as Coumadin (warfarin), given to prevent blood clotting.
  • Mixing alcohol with some drugs is particularly dangerous. Alcohol interacts with most antidepressants and with other drugs that affect the brain. The combination can cause fatigue, dizziness, and slow reactions. Alcohol can increase your risk of stomach bleeding or liver damage when mixed with over-the-counter anti-inflammatory drugs and medications used to treat pain and fever. These drugs include aspirin, ibuprofen, and acetaminophen.

Drug-Condition Interactions

Drug-condition interactions may occur when a medication interacts with an existing health condition. Some examples of drug-condition interactions include:

  • Decongestants, such as pseudoephedrine, found in many cough and cold medicines, can increase blood pressure and may be dangerous for people with hypertension.
  • Beta-blockers, such as Toprol XL (metoprolol) and Tenormin (atenolol), used to treat high blood pressure and certain types of heart disease can worsen the symptoms of asthma and COPD.
  • Diuretics, such as hydrochlorothiazide, can increase blood sugar in people with diabetes.


  • Before starting any new prescription drug or over-the-counter drug, talk to your primary healthcare provider or pharmacist. Make sure that they are aware of any vitamins or supplements that you take.
  • Make sure to read the patient information handout given to you at the pharmacy. If you are not given an information sheet, ask your pharmacist for one.
  • Check the labels of your medications for any warnings and look for the “Drug Interactions” section. Read these warnings carefully.
  • Make a list of all your prescription medications and over-the-counter products, including drugs, vitamins, and supplements.
  • If possible, use one pharmacy for all your prescription medications and over-the-counter products. This way your pharmacist has a record of all your prescription drugs and can advise you about drug interactions and side effects.

Finding Info About Drug Interactions for Medications

The Food and Drug Administration (FDA) is responsible for monitoring drug interactions and side effects and assuring that drugs sold in the United States are safe. The FDA website has useful information about drug safety issues.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Michael Bihari, MD
Michael Bihari, MD, is a board-certified pediatrician, health educator, and medical writer, and president emeritus of the Community Health Center of Cape Cod.