Drug Interactions: What You Need To Know

Suraya Hammoudeh, PharmD

Top Takeaways:

Drug interactions can range from mild to life-threatening.

  • Many interactions are preventable.

  • Lack of communication between older adults and their medical team increases their risk of drug interactions.

  • The best way to prevent drug interactions is to consult your loved one’s PharmD, take medications as prescribed, keep an updated list of all medications taken, and go to follow-up appointments. 

As people get older, they tend to use more medications. In fact, from 2015 to 2016, about 34.5% of adults ages 60 and older were taking five or more prescription drugs according to the CDC. It’s important to be aware of how these different medications may affect the patient when used together. 

Older adults with weak kidney and liver function who take multiple medications are at a higher risk of experiencing drug interactions.

Many adults may believe they are not susceptible to interactions without seeking advice from a physician. According to a report by the National Poll on Healthy Aging by The University of Michigan, while 90% of older adults said they were confident they know how to avoid drug interactions, only 35% of them spoke with a healthcare professional about interactions.


What Are Drug Interactions?

Drugs can help treat or manage diseases and chronic conditions, such as:

  • Hypertension

  • Diabetes

  • High cholesterol

  • Heart disease 

Sometimes, when certain drugs or substances are consumed together, patients experience unwanted side effects and complications due to the chemical makeup of the medications. These are called drug interactions or medication interactions.

4 Types Of Drug Interactions


1. Drug-drug interactions: 

Drug-drug interactions can happen when a drug interacts with another drug. Additional to prescribed medications, these drugs include over-the-counter medications (OTC medications), prescriptions, vitamins, and herbal supplements.

2. Drug-Food interactions: 

These interactions occur when something that the patient eats or drinks alters the effectiveness of a drug by affecting its absorption in the body. In the same way, some medications may affect the absorption of what a patient eats or drinks.

3. Drug-Alcohol interactions: 

Drug-alcohol interactions occur when alcohol consumption affects the concentration of a drug in the body. Alcohol can increase or decrease the amount of a drug in the body, making the substance toxic or ineffective.

4. Drug-Condition Interactions:

Drug-condition interactions occur when a preexisting health condition causes an unwanted reaction to a drug. 

What Are The Most Common Drug Interactions?

Let’s review some of the most common drug interactions to be aware of. 

The drug’s brand name is written first, followed by the generic name in parentheses. Some medications have multiple brand names, so only the most common ones are mentioned below.

Drug-Drug Interactions


  • Jantoven (warfarin), a blood thinner, interacts with many drugs.

    • Taking warfarin with pain relievers, such as Advil and Motrin (ibuprofen), Aleve and Naprosyn (naproxen), and Tylenol (acetaminophen); or the herbal supplement Ginkgo Biloba, increases the risk of serious bleeding.

    • Taking warfarin with St. John’s wort, an herbal supplement used mainly for mental health problems such as depression, may decrease the effect of warfarin and increase the risk for blood clots.

    • The erectile dysfunction drugs Levitra (vardenafil), Viagra (sildenafil), and Cialis (tadalafil), when combined with the heart medication Nitrostat (nitroglycerin), can cause dangerously low blood pressure that may lead to fainting and sometimes death. 

    • When used together, the sedative Xanax (alprazolam) and the antihistamine Benadryl (diphenhydramine) can lead to confusion, impairment in thinking, and difficulty concentrating, especially in older adults.

    • Some antacids and calcium supplements significantly reduce the effectiveness of certain antibiotics. Tetracyclines and fluoroquinolones should not be used alongside antacids or calcium.

    • Mixing opioid drugs, such as OxyContin and Percocet (oxycodone) or Vicodin and Lortab (hydrocodone), with muscle relaxants, such as Xanax (alprazolam) and Valium (diazepam), can lead to difficulty breathing and sometimes death.  

    • Statins used to treat high cholesterol may interact with many drugs.

    • Combining Zocor (simvastatin) and Lopid (gemfibrozil), a fibrate, can increase the risk for rhabdomyolysis, a serious condition where muscle tissues break down. 

    • Combining Lipitor (atorvastatin), Zocor, and lovastatin (Altoprev) with azole antifungals, such as Sporanox (itraconazole) and Diflucan (fluconazole), can also increase the risk of rhabdomyolysis.

    • Certain antidepressants may interact with bronchodilators.

Drug-Food Interactions


These interactions often involve enzymatic inhibitors that prevent balance within the body, possibly leading to toxicity or deficiency. When a particular active ingredient in food acts as an inhibitor substrate in the digestive tract, the body may stop producing a necessary substance or cease limiting the production of a particular substance.

Grapefruit and grapefruit juice can increase the amount of some drugs by inhibiting an enzyme receptor in the intestines responsible for breaking down these drugs, leading to an increased concentration in the blood. Consulting your loved one’s health care provider can help you avoid overlooking these enzyme inhibitions.

Some medications that interact with grapefruit and grapefruit juice include:

  • Statins like Lipitor (atorvastatin), simvastatin, and lovastatin (Altoprev)

    • Immunosuppressants like Prograf (tacrolimus) and Gengraf (cyclosporine)

    • HIV medications like Invirase (saquinavir)

    • Antihistamines like Allegra (fexofenadine)

Foods high in vitamin K, including leafy greens such as kale, cabbage, spinach, broccoli, and collard greens, can decrease the effectiveness of anticoagulants like Coumadin (warfarin) and increase the risk of clotting. 

Eating the same amount of these foods every day ensures Coumadin levels remain stable. 

Many food products act as inhibitors for warfarin, an anticoagulant. Speak with your loved one’s healthcare provider or pharmacist for the most up-to-date list.

  • Dairy products, including milk, cheese, and yogurt, act as inhibitors and can decrease the effectiveness of thyroid medications, especially Synthroid (levothyroxine).  

    • Taking ACE inhibitors, such as Lotensin (benazepril), Prinivil and Zestril (lisinopril), and Accupril (quinapril), with potassium supplements or salt substitutes (these contain potassium), can result in life-threatening complications, especially in older adults.


Drug-Alcohol Interactions


Alcohol often interacts with many prescription medications, nonprescription medications, vitamins, and herbal supplements. The most common interactions include:

  • Combining alcohol with medications for mental health problems, such as Xanax (alprazolam) and Valium (diazepam), can lead to dizziness, drowsiness, fatigue, memory loss, and sometimes death.

  • Antidepressants may have various interaction possibilities with alcohol. Always consult your doctor when your loved one has been prescribed a new antidepressant. 

    • Combining alcohol with nonsteroidal anti-inflammatory drugs, such as Aleve and Naprosyn (naproxen), can lead to liver toxicity and stomach bleeding.

  • Combining stimulants, such as Adderall (amphetamine/dextroamphetamine), Concerta (methylphenidate extended-release), and Ritalin (methylphenidate), with alcohol can lead to heart problems, behavioral problems, alcohol poisoning, and sometimes death.

  • Combining opioids, such as OxyContin and Percocet (oxycodone), and Vicodin and Lortab (hydrocodone) with alcohol can lead to depressed breathing, dangerously low blood pressure, pulse, coma, and sometimes death.


Drug-Condition Interactions


  • Pseudoephedrine, a nasal decongestant found in many cold and cough medications, is not recommended in people with high blood pressure. Pseudoephedrine constricts blood vessels and may lead to dangerously high blood pressure, leading to heart attacks, strokes, and other serious complications. 

  • Thiazide diuretics, a class of drugs used to decrease blood pressure, such as Microzide (hydrochlorothiazide), are not recommended in patients with diabetes as they may increase blood sugar and make diabetes worse.

  • Some beta-blockers, used for hypertension, such as Inderal (propranolol) and Trandate (labetalol), are not recommended in people with asthma and COPD, as they can cause exacerbations. 

How To Prevent Interactions Moving Forward


Here are some issues to discuss with your loved one's healthcare provider and pharmacist regarding drug interactions:

  • Always ask about possible drug interactions for any new drug your loved one is prescribed. Actively engage with the physician as they are prescribing medications. Don’t simply rely on an online checker.

  • Ask if any medications can be stopped. 

  • Speak with them before your loved one takes any over-the-counter medications, vitamins, and supplements. Just because a drug doesn’t require a prescription doesn’t mean it’s safe for everyone to use. 

  • Notify the physician of any known allergies.

  • Always share with the health care provider an updated list of all medications your loved one takes, including:

    • Over-the-counter medicines 

    • Vitamins 

    • Herbal and other dietary supplements

  • Ask if any medications are on the Beers List, which is a list of potentially harmful medications for the elderly. 

    • Ask if they can switch to a safer medicine. Sometimes, even if a drug is on the Beers List, it will be the most appropriate choice for some older adults, and your loved one’s provider will explain this to you. (Whether or not a medication is on the list, never stop taking it before speaking with the patient’s healthcare providers.)  

  • Take medications as prescribed and speak with a healthcare provider or pharmacist before stopping, starting, or changing any medications.  

  • If possible, use only one pharmacy so the pharmacist can keep an updated list of all medications and monitor for any potential drug interactions.

  • Always attend follow-up appointments.

  • Always read the patient information handout provided with each new medication.

Need To Learn More About Interactions?


The Food and Drug Administration (FDA) is the government agency responsible for monitoring drug interactions, side effects, and the safety and effectiveness of drugs. Visit FDA for more information.

Medical  Disclaimer: This article is only a general overview. If you are worried about specific drug interactions, speak with your loved one's healthcare provider or pharmacist. Don’t let fear of drug interactions prevent your loved ones from taking their medications--when used appropriately and with medical supervision, drugs are safe and effective.