Taking an ibuprofen tablet for your headache is harmless, right? Not if you're also taking a blood thinner to prevent a stroke. The combination of the two drugs can cause your blood to become too thin, causing a serious bleeding problem. This is the result of a drug interaction.
Many medicines have powerful ingredients that can interact with other drugs and even some foods and beverages. Drug interactions can cause serious reactions in your body.
Types of drug interactions
There are three main types of drug interactions:
1. Drug-drug interactions occur when one medicine mixes with another and causes a reaction. This can happen with all types of drugs: prescription, over-the-counter, vitamins, supplements or herbs. Possible interactions include:
- One drug can increase or decrease the effect of the other drug.
Example: Combining aspirin and blood thinners - two drugs that prevent blood clots from forming - may cause excessive bleeding. The herb ginkgo biloba may reduce the effectiveness of anticonvulsant drugs used to treat seizures.
- One medicine can increase the side effects of the other drug.
Example: The combination of a sedative (used to treat depression) and an antihistamine can cause excessive drowsiness.
- Combining two medicines can cause a new effect.
Example: Taking a decongestant with some antidepressant medicines may cause heart problems or a severe headache.
2. Drug-food interactions occur when a medicine interacts with something you eat or drink. Some effects include:
- Food can reduce or increase the effects of a drug.
Example: You should avoid foods that contain caffeine - like chocolate - if you take sedative-hypnotics (used to help you sleep.) Caffeine can make these drugs less effective.
- Food can change how medicine is absorbed by the body.
Example: Grapefruit juice can cause levels of some medicines to build up in the body. Cholesterol-lowering medicines called statins are some of the drugs known to interact with grapefruit.
- The combination of the food and drug can create a new effect.
Example: Eating certain cheeses and meats while on monoamine oxidase inhibitors or MAOIs (used to treat depression) can cause a dangerous spike in blood pressure.
- Medications may change how vitamins and minerals are absorbed or removed by the body.
Example: Some diuretics such as furosemide (Lasix) and hydrochlorothiazide cause the body to get rid of too much potassium. In this case, your doctor may tell you to add potassium-rich foods to your diet or take a potassium supplement. Other diuretics, like Triamterene, may let too much potassium build up in the blood. This can lead to serious heart problems. Your doctor may tell you to limit potassium-rich foods if you take this drug.
Mixing alcohol with most drugs is also dangerous. The combination may cause you to feel tired and slow your reactions. Drinking alcohol while on some drugs may raise your risk for liver damage or stomach bleeding. Mixing alcohol with certain medications can even be lethal. If you take prescription or over-the-counter medicine, talk to your doctor before you drink alcohol.
3. Drug-condition interactions occur when a medication interacts with a disease or condition. People with severe kidney disease should not take antacids unless directed by their doctor. Women should avoid certain drugs when pregnant, such as Accutane (used to treat acne), because it can cause birth defects.
Your risk of a drug interaction depends largely on how many medicines you take. The more medicines you take, the greater your chance of a harmful drug interaction. Older adults are at an increased risk because they often take more than one medicine.
Preventing drug interactions
You can lower your risk of a drug interaction by taking these seven steps:
- Read the labels of all medicines before you take them.
- Talk to your doctor or pharmacist before you take any new medicine, whether it's prescription or over-the-counter. Ask if there are any foods, beverages or other drugs you should avoid while taking the medication.
- Keep an up-to-date list of your medications. That includes prescription and nonprescription drugs, vitamins and supplements. Bring the list to your doctor appointments.
- Know what medication your doctor prescribes. If you can't read the doctor's handwriting on the prescription, the pharmacist may not be able to either. Verify the drug name and dose before you leave the doctor's office.
- Take your medication as prescribed. If the directions say to take the drug on an empty stomach, be sure to do so.
- Store all medicines in their original containers so you will not accidentally take the wrong drug.
- Use one pharmacy for all of your medications.
Created on 05/04/2004
Updated on 07/13/2009
- U.S. Food and Drug Administration. Drug interactions: what you should know.
- U.S. Food and Drug Administration. Avoiding drug interactions.
- March of Dimes. Drugs, herbs and dietary supplements.
- Kelly HW, Raissy HH. Principles of pharmacotherapeutics. In: Adkinson NF, Bochner BS, Busse WW, Holgate ST, Lemanske Jr RF, eds. Adkinson: Middleton's Allergy: Principles and Practice, 7th edition, Philadelphia, PA: Mosby Elsevier; 2008.
- National Consumers League. Food and drug interactions.
- U.S. Food and Drug Administration. As you age: you and your medicines.
- Ohio State University Extension. Adverse drug-drug and food-drug medication interactions.