Taking Medicines

Frequently Asked Questions

21. What are the different types of drug interactions?

Drug interactions include

  • drug-drug interactions
  • drug-condition interactions
  • drug-food interactions
  • drug-alcohol interactions.

(Watch this FDA video to learn about avoiding drug interactions. To enlarge the video, click the brackets in the lower right-hand corner. To reduce the video, press the Escape (Esc) button on your keyboard.)

Drug-drug interactions happen when two or more medicines react with each other in your body. The result can be unpredictable and can include unwanted effects, medicines that don’t work properly, or even medicines that become stronger than they should be.

For example, unless your health care professional tells you to, you should not take aspirin if you are taking a prescription blood thinner, such as Coumadin®, also called warfarin, because the combination of the two drugs could lead to dangerous bleeding. Mixing Viagra®, also called sildenafil, and the heart drug nitroglycerin can cause blood pressure to plunge to dangerously low levels.

Even if a product is not called a drug, your body handles it the same way it handles drugs. Some herbal and other substances can interact in potentially dangerous ways with prescription drugs or other over-the-counter products. For example, ginkgo biloba, a botanical product, can reduce the effectiveness of blood-thinning medications and raise the risk for serious complications such as stroke.

Drug-condition interactions happen when a medical condition you already have makes certain drugs potentially harmful. For example, if you have high blood pressure or asthma, taking certain nasal decongestants can cause you to have an unwanted reaction.

Drug-food interactions occur when drugs react with foods or drinks. In some cases, food in the digestive track can affect how a drug is absorbed. Some medicines also may affect the way nutrients are absorbed or used in the body.

Drug-alcohol interactions can happen when the medicine you take reacts with an alcoholic drink. For instance, mixing alcohol with some medicines may cause you to feel tired and slow your reactions.

For more on how medicines and alcohol interact, see Alcohol Use and Older Adults.