The Truth About Drug Interactions: What Everyone Needs to Know

August 5, 2025

Reviewed By: Laureen Lopez Berry, DNP, FNP-C

If you take more than one medication, you are potentially at risk for drug interactions. Drug interactions describe when the efficacy or safety of one medication is affected by another medication, multiple other medications, medical conditions, food, beverages, or supplements [1]. As the number of medications you take increases, so does your risk for drug interactions [2]. Seniors are at particularly high risk for drug-drug interactions because they tend to take multiple medications for chronic conditions [3]. In this guide, we’ll go over the types of interactions, the most common interactions, and warning signs to empower seniors to identify and prevent the dangerous effects of drug interactions.

Understanding Drug Interactions: Beyond the Basics

Despite popular belief, drug interactions don’t only occur when one drug doesn’t react well with another. Other less-suspected causes, like eating certain foods, can cause dangerous interactions with your medications. The types of drug interactions include [4]:

Drug-drug interactions occur when one medication affects another medication (or multiple medications). This includes both prescription and over-the-counter medications.

Drug-food/beverage interactions occur when a food or drink you consume affects a medication you take.

Drug-supplement interactions occur when a supplement or vitamin you take affects a medication you take.

Drug-condition interactions occur when a medical condition you have affects a medication you take.

Drug interactions occur because certain medications can alter the way your body processes others [5]. For example, ingredients and chemicals in one drug can increase or decrease how much, how quickly, and how effectively your body absorbs other drugs.

Not everyone is at equal risk for drug interactions. Seniors and individuals who take multiple medications at once are the most vulnerable to the dangers of drug interactions [6]. However, anyone can experience a drug interaction of any degree [7].

Minor drug interactions occur when an interaction limits the effectiveness of a medication.

Moderate drug interactions occur when the symptoms of an individual’s conditions significantly worsen due to decreased effectiveness of the drug or higher prevalence of side effects.

Severe drug interactions occur when the effects of a drug interaction are life-threatening or require medical intervention.

Common High-Risk Medication Combinations to Avoid

It’s important to check your specific medication labels and consult with your healthcare provider about potential drug interactions. However, the following are common high-risk combinations that increase the chance of a serious interaction:

Interactions with blood thinners: Blood thinners help prevent blood clots, which can reduce the risk of serious conditions such as heart attacks, strokes, and pulmonary embolism [8]. However, these medications can interact with certain supplements and over-the-counter drugs, increasing the risk of internal bleeding. Substances such as ginkgo biloba, garlic, high doses of fish oil, and NSAIDs (nonsteroidal anti-inflammatory drugs, like ibuprofen and naproxen) can enhance the anticoagulant effect. These interactions can be dangerous and should be closely monitored. Patients taking blood thinners should always consult a healthcare provider before starting any new medication [8] Patients taking blood thinners, especially apixaban or rivaroxaban, should also avoid grapefruit and grapefruit juice unless cleared by their provider. Even though interactions with warfarin are less consistent, caution is still warranted [9].

Interactions with selective serotonin reuptake inhibitors (SSRIs): SSRIs, also commonly called antidepressants, increase the level of serotonin in the brain to treat mental health disorders like depression and anxiety [10]. Consuming certain substances while taking an SSRI can increase the risk of developing serotonin syndrome, which is when the body produces too much serotonin, leading to serious side effects [11]. These substances include, but are not limited to, St. John’s wort, triptan medications (for migraines), and some prescription nausea medications [12].

Interactions with blood pressure medications: Blood pressure medications, also called antihypertensives, work to treat hypertension. Taking hypertensives with NSAIDs may cause adverse effects [13].

Food and Medication: Unexpected Interactions in Your Kitchen

Grapefruit and Medications: A Surprising Danger

Grapefruit, the delicious and seemingly harmless fruit, actually has some serious dangers when it comes to drug interactions. You may have noticed that some of your medication labels advise you to avoid eating grapefruit while using the medication. Why is this? Your body breaks down, or metabolizes, many types of medications by using an enzyme in the small intestine [14]. Grapefruit can block this enzyme, so your body can’t metabolize the medication as easily. This means that more than the safe amount of the medication can stay in your body, and for too long.

Check your specific medication’s label and ask your doctor to see if it’s safe to eat grapefruit while taking it. The medication groups that are most commonly affected by grapefruit include, but are not limited to, drugs used to treat high cholesterol, high blood pressure, anxiety, Crohn’s disease, ulcerative colitis, and abnormal heart rhythms [14].

Although grapefruit is the main culprit for these adverse drug effects, other citrus fruits can cause similar issues. As a safe measure, if your medication says to avoid eating grapefruit, you should also avoid eating pomelos, tangelos, and Seville oranges [15]. As far as non-citrus fruits, though, you’re safe to enjoy!

Other Common Food-Drug Interactions

There are some other foods you’ll want to check with your doctor about before starting certain types of medications. These foods include:

Dairy products: Avoid consuming dairy products, like milk, cheese, yogurt, and butter, for 3 hours after taking antibiotic medications, as dairy can affect how the body absorbs antibiotics [16].
Leafy greens: Eating large amounts of leafy greens and other foods high in Vitamin K can interfere with the way that blood thinners and anticoagulant medications work [17].
Tyramine-rich foods: Those who take monoamine oxidase inhibitors (MAOIs), a type of antidepressant, should avoid foods high in tyramine, which include fermented, aged, overripe, or spoiled foods [18]. This is because MAOIs make the body unable to break down tyramine, and too much tyramine can lead to issues like high blood pressure.
High-sodium foods: Eating foods high in sodium while taking painkillers can increase the risk for high blood pressure and heart disease, especially among seniors [19].

Supplement and Over-the-Counter Medication Risks

Similar to the way you must avoid certain foods while taking some medications, you may need to do the same for supplements and over-the-counter medications. Here is what to look out for:

Check if any herbal supplements interact with your medication. Herbal supplements, such as St. John’s wort and Ginkgo biloba, to name a few, have been shown to have negative effects on multiple medications’ efficacy and safety [20].
Assess whether common vitamin supplements could affect your medication. Vitamins may seem harmless, but some can disrupt the balance of your medication [21].
Ask your doctor before taking over-the-counter pain relievers with your medication. Painkillers may seem safe if they can be bought over the counter, but this does not mean they won’t interact with your prescription medications. Always ask your doctor about the potential interactions between your new medication and over-the-counter drugs—they may cause serious adverse events [22].
Be careful about natural sleep aids. Many people use natural sleep aids, like melatonin, to help them fall asleep at night. However, natural sleep aids can sometimes interact with medications and make you overly sedated [23].

Using Drug Interaction Checkers Effectively

There are many free and reputable online tools for checking if there are any potential interactions with your new medication. For example, the Drugs.com interaction checker shows a detailed list of all possible interactions. To use it, simply enter the name of your new medication as well as the name(s) of the medication(s) you are already taking. The checker will assess any potential interactions between all of these medications.

Remember, you should always check with your doctor and/or pharmacist if you have any questions about drug interactions or want to confirm the results of your online drug interaction checker.

Creating a Personal Medication Safety System

To create your own medication safety system, organization is key. Start by creating a complete list of all the medications (both prescription and over-the-counter) and supplements you take, as well as all the conditions you have. Bring this list to your next doctor’s appointment and ask them to check any new prescriptions against your list. Your pharmacist can also help you understand potential drug interactions.

Special Population Considerations

Older Adults and Multiple Medication Risks

As previously mentioned, seniors are at increased risk for drug interaction vulnerability. Older adults process medications differently than younger individuals, which may exacerbate their side effects and potential interactions with other substances or conditions. For example, kidneys tend to weaken as we age, and this can affect older adults’ ability to remove medications as quickly and effectively [24].

Certain medications prescribed to seniors for common conditions have high interaction risks, such as drugs for managing blood pressure, seizures, anxiety, and chronic pain [24]. To best understand the interactions your medications may have, have an in-depth conversation with your healthcare provider and/or pharmacist. If you are concerned about the number of potential interactions, consider reducing the number of prescription medications you take and talk about this possibility with your doctor before making any changes.

Chronic Condition Medication Interactions

Chronic conditions common among seniors can increase the risk of dangerous drug interactions. Some of these chronic conditions include:

Diabetes medications have high interaction rates with cardiac drugs, pain relievers, antibiotics, diuretics, and more [25].
Heart disease treatments, such as statins, can interact with fibrates, transplant medications, blood thinners, HIV medications, and more [26].
Pain management medications may interact with medications for hypertension, lithium, narcotics, and alcohol [27].
Mental health medications, such as SSRIs, have common interactions with blood thinners, NSAIDs, and other antidepressants [28].

When to Seek Help: Warning Signs and Emergency Response

Even if you read the drug label, use an interaction checker, and speak with your healthcare provider, there’s still a chance that medication interactions can occur. Signs and symptoms of a serious medication interaction can range from mild to serious. Interaction symptoms include rashes on the skin, bruising, bleeding, swelling, nausea, confusion, abnormal heartbeat, and more [29]. If you experience any of these symptoms, contact your doctor immediately. Call for emergency help (911) if you experience symptoms of an overdose or allergic reaction, and/or severe side effects. As a general rule of thumb, you should always seek emergency care rather than non-urgent care when your symptoms require immediate care, like trouble breathing, bleeding that won’t stop, severe chest pain, unconsciousness, or inability to move [30].

Your Medication Safety Action Plan

Now that you understand the dangers of drug interactions, we hope you will take the key steps to implement medication safety measures into your everyday life. Remember, your care team and loved ones are there to answer any questions you may have and support you throughout the process. For more support on medication management and wellness tips, contact Greater Good Health today.

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