We live in a world where incredible drugs exist to treat many conditions that seemed untouchable in the past.

In a report that looked at U.S. prescription drug use in the years 2013 to 2016, the Centers for Disease Control and Prevention (CDC) found that an estimated 48.4 percent of Americans used at least one prescription in the past 30 days.

It’s encouraging to know that there are options to address many of our common ailments. However, the impressive availability of medications also increases the possibility of drug interactions.

Drug interactions involve combinations of 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 each of your doctors know 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 using 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. Let’s explore each one a little further.


A drug-drug reaction is when there’s an interaction between two or more prescription drugs.

One example is the interaction between warfarin (Coumadin), an anticoagulant (blood thinner), and fluconazole (Diflucan), an antifungal medication. Taking these two drugs together can lead to a potentially dangerous increase in bleeding.

Drug-nonprescription treatment

This is a reaction between a drug and a nonprescription treatment. These include over-the-counter (OTC) medications, herbs, vitamins, or supplements.

An example of this type of interaction can occur between a diuretic — a drug that attempts to rid the body of excess water and salt — and ibuprofen (Advil). The ibuprofen may reduce the diuretic’s effectiveness because ibuprofen often causes the body to retain salt and fluid.


This happens when food or beverage intake alters a drug’s effect.

For example, some statins (used to treat high cholesterol) can interact with grapefruit juice. If a person who takes one of these statins drinks a lot of grapefruit juice, too much of the drug may stay in their body, increasing their risk for liver damage or kidney failure.

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.


Certain medications shouldn’t be taken with alcohol. Often, combining these drugs with alcohol can cause tiredness and delayed reactions. It can also increase your risk for negative side effects.


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. This is a potentially dangerous interaction for people with high blood pressure (hypertension).

Another example is metformin (a diabetes drug) and kidney disease. People with kidney disease should use a lower dosage of metformin or not take it at all. This is because metformin can accumulate in the kidneys of people with this disease, increasing the risk of severe side effects


Some medications can interfere with specific laboratory tests. This can result in inaccurate test results.

For instance, tricyclic antidepressants have been shown to interfere with skin prick tests used to determine whether someone has certain allergies.

While it’s important to educate yourself on your potential for 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. Specifics about your drugs, including dosage, formulation, and how you take them, can also make a difference.

The following factors of an individual’s medical history influence possible drug interactions:


Variations in individual genetic makeup can make the same drug work differently in different bodies.

As a result of their particular genetic code, some people 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 will know which drugs require genetic testing to find the correct dosage for you.


Some drugs are dosed according to how much a person weighs.

Weight changes could affect dosage and also increase or decrease the risk of drug interactions. So if you have a substantial change in your weight, you could need a different dosage of some medications.


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.

Sex (male or female)

Differences between the sexes, such as anatomy and hormones, can play a part in drug interactions.

For example, the recommended dose of zolpidem (Ambien) given to women was lowered to half the amount prescribed to men. This happened after research found that women were more likely to have high levels of the drug in their system in the morning, when it could impair activities like driving.

Lifestyle (diet and exercise)

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 treat symptoms.

Exercise can also change how medications work.

For example, people who use insulin to treat diabetes can experience hypoglycemia (low blood sugar) during exercise. So they may need to adjust the time 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 mention to your doctor that you smoke if they’re recommending you start a new medication.

If you’re thinking about quitting smoking, your doctor can work with you to come up with a personal plan to stop.

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 your doctor needs to know all the drugs you’re taking before 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 to process them more quickly over time. So dosages may have to be adjusted if they are taken for a long time. Two examples are pain drugs and antiseizure drugs.


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 exact 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 with your doctor first.

How the drug is taken or administered

There are many different ways a drug can be administered. Some common ways we take drugs include orally (by mouth), by injection, and topically (applied to the skin). The way medications enter the body can greatly alter the resulting effects.


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.

The order in which medications are taken

Some drug interactions can be reduced or eliminated if the drugs are taken at different times.

Certain drugs may affect the absorption of other drugs when taken one before the other. Antacids like calcium tablets can prevent the absorption of the antifungal medication ketoconazole, for example.

Speaking with your doctor or pharmacist is the best way to stay informed about your medications.

But you should always read all drug labels and patient drug information you receive, whether the drug is prescription or OTC. These will help you to better understand your drugs, and it may also prevent interactions.

OTC drug labels

OTC drug labels will include the following information:

  • Active ingredient and purpose: Lists the ingredients in the drug that serve therapeutic purposes. The “Purpose” section will say what each ingredient does (for example, nasal decongestant, antihistamine, pain reliever, fever reducer).
  • Uses: A short description of what symptoms or conditions the drug is meant to treat.
  • Warnings: The section that provides important information about using the drug safely. It will say when to stop or not use the drug and when to consult with a doctor about its use. Side effects and potential interactions are also listed here.
  • Directions: Instructions for how much of the medication should be taken and how often. If there are any special instructions for how to take the drug, they will be listed here.
  • Other information: This section often has information about how to properly store the drug. It may also give additional information about certain ingredients the drug contains, such as the amount of calcium, potassium, or sodium. These details can be important for people with allergies or dietary restrictions.
  • Expiration date: Date up to which the manufacturer guarantees the safety and effectiveness of the drug.
  • Inactive ingredients: List of ingredients in the drug that don’t serve a therapeutic purpose, such as colorings and flavorings.
  • Manufacturer contact information: You can usually call the manufacturer on a toll-free line if you have questions about the drug. Most companies staff these lines Monday through Friday.

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. The package insert describes:

  • how the drug works and information about clinical trials for the drug
  • how to take the drug and any precautions (such as whether it shouldn’t be taken with food)
  • what conditions the drug is used to treat
  • warnings about potential side effects or adverse reactions
  • possible interactions with other drugs, supplements, foods, or beverages
  • dosage information and instructions on what to do in case of an overdose
  • other information, such as what the drug looks like and how to store it

The prescription stock bottle may also have warning labels in the form of colorful stickers located directly on bottles. These have information about 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 to 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 of the medications you are taking.

Have a clear conversation about potential foods, OTC drugs, and diseases that could cause problems when combined with your medications.

Some questions to ask:

  • How exactly does this drug work in my body? What potential side effects may 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?
  • (If applicable) Can I take this drug while I’m pregnant or breastfeeding?
  • Can this drug be crushed or chewed if I find it hard to swallow, or mixed with food or drink to mask its taste?

If you have any concerns or questions about medications you’re taking or planning to take, consult with your doctor. In particular, women who are pregnant or breastfeeding should check with their doctor before taking any new medications.