Drug Interactions

What is a drug interaction?

A drug interaction is a change in the effect of a drug caused by some other substance. In some cases, there is a change in the helpful effects of a drug and in other cases there is a change in side effects. It is important to remember that alcohol and tobacco, as well as prescription and nonprescription medicines, can be involved in drug interactions. Vitamins, natural remedies, and certain foods may also interact with drugs.

There are many different types of drug interactions, and not all of them occur in every case. Sometimes, drug interactions are helpful. Drug combinations may be prescribed that allow lower doses to be used. This reduces the chance of side effects.

How does it occur?

Drug interactions fall into 2 broad categories:

Drug/drug interactions occur when 2 or more drugs react with each other. For example, one drug might decrease the effectiveness of another drug. Some medicines are more likely to interact with other drugs and cause serious problems, such as severe bleeding or heart rhythm problems. Two common examples of such drugs are warfarin (Coumadin) and digoxin (Lanoxin).
Drug/food interactions result from drugs reacting with foods or beverages. For example, drinking alcohol while taking some drugs may cause you to feel tired or it may slow your reactions. This can make driving a car or operating machinery dangerous. Grapefruit juice affects the way some medicines work and may increase the risk of side effects.

Drugs may also work differently if you have an existing medical condition such as diabetes, heart disease, or asthma. Some drugs may be harmful for people with certain conditions. For example, taking a nasal decongestant can raise your blood pressure, which may be harmful if you already have high blood pressure.

Any time you take a new medicine, there is a possibility it will interact with other medicines you take. Your health care providers and pharmacist need to be aware of all the medicines and herbal remedies you take to avoid problems such as drug interactions, especially if you:

take several different medicines
see more than one health care provider
have certain health conditions.

Keep a list of your current medicines with you at all times. Providers can then check the list to see if any drug interactions might occur.

What can I do to prevent drug interactions?

Before taking a drug, ask your health care provider or pharmacist these questions:

Can I take it with other drugs?
Should I avoid certain foods, beverages, or other products?
How will the drug work in my body?
What are possible signs of a drug interaction I should know about?

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

HIA File MED4263F.HTM Release 9.0/2006