Drug interactions can occur when someone takes a medication with other substances that alter the medication’s effect on the body. This can cause the medication to be less or more potent than intended or result in unexpected side effects.
If you use multiple medications, have certain health conditions, or see more than one doctor, you should be especially mindful of your medications. You also need to make sure that all of your doctors are aware of all of the drugs, herbs, supplements, and vitamins you’re using.
Even if you take only one medication, it’s a good idea to talk with your doctor or pharmacist about what you’re taking to identify possible interactions. This advice applies to both prescription and nonprescription drugs.
There are several different types of drug interactions to be aware of.
Drug-drug
A drug-drug reaction is when there’s an interaction between:
- two or more prescription drugs
- a prescription drug and a nonprescription drug
- two or more nonprescription drugs
One example is the interaction between the prescription anticoagulant (blood thinner) medication warfarin (Coumadin) and fluconazole (Diflucan), an antifungal prescription medication. Taking these two drugs together can lead to a potentially dangerous increase in bleeding.
Nonprescription treatments that may also interact with prescription medications or each other include over-the-counter (OTC) medications, herbs, vitamins, and supplements.
An example of this type of interaction can occur between a prescription or OTC diuretic — a drug that helps the body expel excess water and salt — and ibuprofen (Advil). Ibuprofen may reduce the diuretic’s effectiveness because ibuprofen often causes the body to retain salt and fluid.
Drug-food
This happens when food or beverage intake alters a drug’s effect.
For example, some statins (used to treat high cholesterol)
Another potential outcome of the statin-grapefruit juice interaction is rhabdomyolysis. This is when skeletal muscle breaks down, releasing a protein called myoglobin into the blood. Myoglobin can go on to damage the kidneys.
Drug-alcohol
Certain medications should not be mixed with alcohol. Often, combining these drugs with alcohol can increase the risk of adverse side effects, including tiredness and delayed reactions.
For example,
Drug-disease
This interaction is when the use of a drug alters or worsens a condition or disease. Additionally, some medical conditions can increase the risk of side effects from specific drugs.
For example, some decongestants that people take for colds can increase blood pressure and are not suitable for people with hypertension (high blood pressure).
Another example is the diabetes drug metformin (Glumetza) and kidney disease. People with kidney disease may need a
Drug-laboratory
Some medications can interfere with specific laboratory tests and may result in inaccurate test results.
For instance, tricyclic antidepressants may interfere with skin prick tests used to determine whether someone has certain allergies.
While it’s important to educate yourself on your potential for experiencing drug interactions, understand that this information doesn’t tell you everything you need to know. Just because a drug interaction can occur doesn’t mean it will.
Personal traits can play a role in whether a drug interaction will happen and if it will be harmful.
Genetics
Variations in individual genetic makeup can make the
Some people — because of their specific genetic code — process certain medications more quickly or more slowly than others. This may cause the drug levels to go down or go up more than expected. Your doctor knows which drugs require genetic testing to find the correct dosage for you.
Weight
Some drugs are dosed according to how much a person weighs.
Weight changes could affect dosage and the risk of drug interactions. So if you experience a substantial change in your weight, you may need a different dosage of some medications.
Age
As we age, our bodies change in many ways, some of which may affect how we respond to medications. The kidneys, liver, and circulation system may slow down with age. This can slow the breakdown and removal of drugs from our bodies.
It’s good to ask your doctor about possible interactions at any age, but especially if you’re 65 or older, talk with your doctor about everything you’re taking.
Sex assigned at birth
Differences between the sexes, such as anatomy and hormones, can play a part in drug interactions.
For example, a 2021 study notes that men metabolize zolpidem (Ambien) faster than women.
Lifestyle (nutrition and physical activity)
Certain diets can be problematic when combined with medication.
For example, research has shown that high fat intake can reduce the response of bronchodilators, which people with asthma use to manage their symptoms.
Exercise can also change how medications work.
For example, people who take insulin to treat diabetes can experience hypoglycemia (low blood sugar) during exercise. So they may need to adjust when they eat and take their insulin to offset the drop in blood sugar.
Smoking cigarettes can also affect the metabolism of some drugs. Be sure to tell your doctor whether you smoke if they’re recommending you start a new medication.
If you’re thinking about quitting smoking, your doctor can help you create a personal plan with actionable steps to help you stop.
High levels of vitamin K in the diet
How long the drug is in your body
Many factors affect the speed at which the body absorbs and processes drugs. The right dose for each person may depend on such factors and may be higher or lower than the typical dose.
This is another reason why it’s important to tell your doctor about all the drugs you’re taking when they’re considering prescribing a new medication.
How long you’ve been taking the drug
The body can become tolerant to some medications, or the drugs themselves may help the body process them more quickly over time. So dosages of certain medications, including pain medications and antiseizure drugs, may need to be adjusted if they’re taken for a long time.
Dose
The term “dose” is the amount of medication prescribed to be taken or administered. (You may sometimes hear the term “dosage,” which refers to an amount of medication given at specific periods of time — for example, once a day.)
Two people taking the same drug may be prescribed different doses. Calculating the proper dose requires precision, so you shouldn’t alter how much of a medication you take without consulting your doctor first.
How the drug is taken or administered
There are many different drug administration methods. Some common ways drugs are taken include orally (by mouth), by injection, and topically (applied to the skin). The way medications enter the body can alter the resulting effects.
Formulation
The formulation of a medication is the specific mixture of ingredients the drug contains. A medication’s formulation is important because it can determine, in part, how the drug acts in the body as well as its effectiveness.
For example, doctors prescribe intravenous vancomycin
The order in which medications are taken
Taking drugs at different times can reduce the risk of adverse interactions.
Certain drugs may affect the absorption of other drugs when taken one before the other. For example, antacids like calcium tablets can prevent the absorption of the antifungal medication ketoconazole (Recorlev).
Learn more about specific drug interactions for these common medications:
Speaking with your doctor or pharmacist is the best way to stay informed about your medications. But always reading all drug labels and patient drug information you receive is also necessary, whether the drug is prescription or OTC.
Doing this can help you better understand your medications, and it may also prevent interactions.
OTC drug labels
OTC drug labels typically include the following information:
- active ingredient and purpose
- uses
- warnings
- directions
- other information
- expiration date
- inactive ingredients
- manufacturer contact information
The “warnings” section often has more information about potential interactions. If any of the information is unclear, a pharmacist can help.
Prescription drug labels
There are two kinds of prescription labels — package inserts and patient package inserts (PPI). The Food and Drug Administration (FDA) regulates the format and standards of both types of labels.
You may also see a package insert called the prescribing information. It’s a detailed document containing information about the drug and is usually found inside or attached to the prescription stock bottle.
To learn more about a prescription drug, ask for the package insert. Among other things, the package insert will list possible interactions with other drugs, supplements, foods, or beverages.
The label on the prescription bottle itself may also have warnings or colorful stickers that describe side effects and potential interactions.
The PPI is more familiar to most people. It’s the information that’s given with the medication that’s dispensed directly to you. The PPI includes detailed information about the use of the drug, which is written more clearly than most package inserts.
Additionally, your prescription label should contain your name, your doctor’s name, and the name of the drug, along with the strength, dose, directions, expiration date, and other identifying information. This brief information is there to remind you about how to take the drug.
Talk with your doctor or pharmacist to get the most accurate and up-to-date information about your personal risk of drug interactions. Make sure they know all the medications you’re taking.
Have a clear conversation about potential foods, drinks, OTC drugs, and health conditions that could cause problems when combined with your medications.
Questions to ask your doctor or pharmacist
- How exactly does this drug work in my body? What potential side effects could I experience?
- Can I take this medication with my other prescriptions? If so, should I take it at a different time than my other medications?
- I also take the following OTC drugs, herbs, vitamins, or supplements. Is this drug safe to take with them?
- Are there any specific foods or beverages that I should avoid when I’m taking this drug? If so, why?
- What potential effect could alcohol consumption have while taking this drug?
- Can you also explain the signs of a drug interaction that I should look out for?
- What should I do if I experience severe side effects or a drug interaction?
- I’d like more information about this drug. Can you provide me with a copy of the package insert? If not, where can I find it online?
- Can this drug be crushed or chewed if I find it hard to swallow, or mixed with food or drinks to mask its taste?
If you have any concerns or questions about medications you’re taking or planning to take, consult your doctor. In particular, people who are pregnant or nursing should check with their doctor before taking any new medications.
While you’re taking a medication, it may help to keep a written record of any symptoms you notice.
Be sure to list your symptoms in detail, including when they started and if they occur at particular times of the day or around certain activities. Also, list the foods and beverages you consume, as well as any other supplements, vitamins, and OTC or prescription medications.
Your doctor can use this information to determine whether your symptoms are related to the drug itself or a possible interaction with something else you’re taking.
Drugs can have many interactions with other drugs, foods, drinks, or other substances. To be safe, it’s best to tell a healthcare professional about everything you’re taking and ask about any possible interactions that may occur.