Dr. Steven Malen graduated with a dual degree: Doctor of Pharmacy (PharmD) and Master of Business Administration (MBA) from the University of Rhode Island. Over his career, he has worked as a clinical pharmacist in the retail, specialty, and compounding sectors. He specialized and taught on topics from vaccines to veterinary compounding. Dr. Malen has also written a science fiction novel and taught and co-founded the concept of Patient Empowered Blockchain (P.E.B.). Currently, Dr. Malen continues to write, teach, and consult various companies in the healthcare sector.


Topic Overview

This course is designed to provide healthcare professionals with the knowledge and tools needed to identify and prevent potential drug interactions between over-the-counter (OTC) products and prescription medications. Understanding the mechanisms of OTC and prescription medication interactions is crucial for healthcare professionals to ensure patient safety and optimize treatment outcomes. Thereafter, strategies can be employed to identify potential interactions before they occur. These strategies include effective communication between healthcare providers and patients and the use of resources that list and describe potential drug-drug interactions.


Accreditation Statement:




RxCe.com LLC is accredited by the Accreditation Council for Pharmacy Education (ACPE) as a provider of continuing pharmacy education.


Universal Activity Number (UAN): The ACPE Universal Activity Number assigned to this activity is 

Pharmacist 0669-0000-23-086-H05-P

Pharmacy Technician 0669-0000-23-087-H05-T

Credits: 1 hour of continuing education credit


Type of Activity: Knowledge


Media: Internet/Home study Fee Information: $4.99

Estimated time to complete activity: 1 hour, including Course Test and course evaluation


Release Date: June 17, 2023 Expiration Date: June 17, 2026


Target Audience: This educational activity is for pharmacists.


How to Earn Credit: From June 17, 2023, through June 17, 2026, participants must:


Read the “learning objectives” and “author and planning team disclosures;”

Study the section entitled “educational activity;” and

Complete the Course Test and Evaluation form. The Course Test will be graded automatically. Following successful completion of the Course Test with a score of 70% or higher, a statement of participation will be made available immediately. (No partial credit will be given.)

Credit for this course will be uploaded to CPE Monitor®.


Learning Objectives: Upon completion of this educational activity, participants should be able to:


List potential risks associated with mixing common over-the-counter (OTC) products with prescription medications

Identify common types of drug interactions that can occur

Describe effective communication strategies for counseling patients on the safe use of OTC products in combination with prescription medications



The following individuals were involved in developing this activity: Steven Malen, PharmD, MBA, and Pamela Sardo, PharmD, BS. Pamela Sardo, Pharm.D., B.S., was an employee of Rhythm Pharmaceuticals until March 2022 and has no conflicts of interest or relationships regarding the subject matter discussed. There are no financial relationships relevant to this activity to report or disclose by any of the individuals involved in the development of this activity.


© RxCe.com LLC 2023: All rights reserved. No reproduction of all or part of any content herein is allowed without the prior, written permission of RxCe.com LLC.



Using over-the-counter (OTC) products alongside prescription medications is becoming increasingly common in healthcare. While OTC products can effectively relieve many ailments, the risks associated with mixing these products with prescription medications cannot be ignored. The potential for drug interactions between these products can seriously threaten patient safety and result in adverse drug events. Therefore, healthcare professionals need to have a comprehensive understanding of the risks associated with combining OTC products and prescription medications and effective strategies for mitigating these risks. This course aims to provide healthcare professionals with the knowledge and tools necessary to evaluate the potential risks associated with mixing OTC products with prescription medications, identify some of the common types of drug interactions that can occur, and develop effective communication strategies for counseling patients on the safe use of OTC products in combination with prescription medications.


Overview and Common OTC Products


Over-the-counter products are widely used to treat various symptoms and ailments, and their use has become an integral part of self-care. In the U.S., OTC medications are available to people without a prescription.1 According to the U.S. Food and Drug Administration, more than 300,000 OTC drug products are on the market, and over 80 different therapeutic classes of drugs, e.g., analgesics or antacids.2


Over-the-counter products pose a significant risk of drug interactions and medication errors that may lead to harm, especially in pediatric and elderly patients.1 The extent of this issue is great. An estimated one-third of older adults reportedly use OTC drugs, and this percentage increases to one-half with people 75 to 85 years of age.1 Some older adults use two or more OTC drugs.1 Gilson, et al. (2021) believe that “over one million older adults are in physical jeopardy from harms related to the use of 2 or more OTC medications.”1

Of the ten drugs most frequently used by the public, four of them are available OTC.3 These four OTC drugs are pain relievers ibuprofen, aspirin, and acetaminophen, and diphenhydramine, an antihistamine.3 These drugs are also available in multiple-ingredient preparations, which increases the risk of a potentially dangerous overdose.3 Other common OTC products include cough and cold medications, antacids, and herbal supplements. These products can interact with prescription medications in ways that may alter their efficacy or cause adverse effects. Therefore, it is crucial for healthcare professionals to have an understanding of the common types of OTC products that can interact with prescription medications.4-6


Mechanisms of OTC and Prescription Medication Interactions


Drug interactions occur when the presence of a drug alters the effects of another medication. Understanding the mechanisms of OTC and prescription medication interactions is crucial for healthcare professionals to ensure patient safety and optimize treatment outcomes.


Drug Metabolism and Pharmacokinetics


Pharmacokinetics is sometimes described as what the body does to a drug. For example, pharmacokinetics is seen in a drug’s half-life and how the body metabolizes it. Pharmacokinetic drug-drug interactions occur when a “precipitant” drug interferes with an “object” drug’s kinetics, e.g., absorption, distribution, metabolism, or excretion.4 For example, many medications undergo metabolism in the liver, primarily by enzymes belonging to the cytochrome P450 (CYP) family. Interactions can arise when a drug inhibits or induces these enzymes, leading to altered levels of other medications in the body.


A prescription medication that inhibits a specific CYP enzyme may increase the concentration of an OTC medication metabolized by the same enzyme, potentially causing adverse effects or therapeutic failure.7 For example, curcumin, an ingredient extracted from turmeric, is an over-the-counter product used for its antioxidant and anti-inflammatory activity.8 It can induce pharmacokinetic alterations, such as changes in maximum concentration when

used with cardiovascular drugs, anticoagulants, or antihistamines.8 The underlying mechanisms include the inhibition of cytochrome P450 enzymes. Some medicinal plants, such as Ginkgo and garlic, have been known to cause uncontrollable bleeding when used with the anticoagulant warfarin.8


St. John's wort and over-the-counter product that is sometimes used for depression or insomnia has interactions of importance.9 Use of St. John’s wort, a CYP3A4 inducer, in combination with zolpidem, a prescription for insomnia, may decrease blood levels of zolpidem and is not recommended.9


Drug-drug Interactions and Pharmacodynamics


In addition to drug metabolism, pharmacodynamics also plays a role in medication interactions. Pharmacodynamics refers to how drugs interact with target receptors or enzymes in the body to produce a therapeutic effect. Drug- drug interactions can occur when two medications have similar or opposing effects on the same receptor or enzyme system. For instance, if an OTC medication and a prescription drug target the same receptor, they may compete for binding, leading to reduced efficacy or enhanced side effects. Conversely, if two medications have opposing effects, such as one medication increasing heart rate and another lowering it, their combination may result in unpredictable and potentially dangerous cardiovascular effects.10 In these cases, either drug may act as a precipitant or object drug, or they may act as both.4


Factors that Affect Drug Interaction Severity


Several factors influence the severity of drug interactions. One crucial factor is the dose and duration of medication use. Higher doses or longer durations of therapy can increase the likelihood of interactions occurring. Additionally, individual patient characteristics, such as age, liver or kidney function, and genetics, can impact the severity of interactions. For example, elderly patients may be more susceptible to drug interactions due to age-related changes in drug metabolism and elimination. Furthermore, genetic variations in drug-metabolizing enzymes can affect an individual's response to medications, potentially leading to interactions. Understanding these factors allows healthcare

professionals to assess the risk of interactions and make informed decisions regarding medication regimens.11


Over-the-counter calcium carbonate antacids can interact with the antibiotic tetracycline. This combination leads to binding. Absorption of tetracycline is impaired by these antacids. The antibiotic can become less effective, and combined use is not recommended.12


Comprehending the mechanisms of OTC and prescription medication interactions is essential for healthcare professionals. Factors such as drug metabolism and pharmacokinetics, drug-drug interactions and pharmacodynamics, and patient-specific characteristics can all influence the occurrence and severity of interactions. Healthcare providers should stay updated on the latest research and guidelines to identify potential interactions and take appropriate measures to mitigate risks. By considering these factors, healthcare professionals can optimize patient care and ensure the safe and effective use of medications.13


Identifying and Preventing OTC and Prescription Medication Interactions


Identifying and preventing medication interactions between OTC and prescription medications is crucial for promoting patient safety and optimizing therapeutic outcomes.14-17 Various strategies can be employed to identify potential interactions before they occur. One approach uses comprehensive medication reconciliation, where healthcare providers review the patient's complete medication list, including OTC medications, supplements, and herbals, to identify potential interactions. Utilizing electronic health record systems and medication interaction software can aid in flagging potential interactions based on known drug-drug interaction databases. These resources provide valuable information on the mechanisms and severity of interactions, allowing healthcare professionals to make informed decisions regarding medication regimens.

Patient education and engagement are also vital in preventing medication interactions. Patients should be encouraged to inform their healthcare providers about all medications they are taking, including OTC products. Patients need to understand the potential risks associated with combining certain medications and the importance of following dosage instructions.


Pharmacists are crucial in counseling patients and providing information on potential interactions. They can offer guidance on appropriate OTC medication choices, highlight potential interactions, and educate patients on the importance of reading labels and package inserts. Pharmacy staff members can observe individuals when they are purchasing OTC drugs and then engage in conversations with them and make recommendations.3


Another approach may be redesigning pharmacy aisles so that pharmacists and technicians can interact more with patients, older adults, or parents of young children regarding OTC drug purchases.1,3,18 The redesign of store aisles and greater interaction with pharmacy staff are intended to decrease the potential misuse of these drugs and provide patients with more information and awareness about the possible dangers of OTC medication.


Healthcare professionals can also take preventive measures by considering alternative medications or adjusting doses when potential interactions are identified. In some cases, selecting medications with different metabolic pathways or avoiding combinations known to have significant interactions can minimize the risk. Additionally, dose adjustments may be necessary if one medication alters the metabolism or elimination of another. Monitoring patients closely for signs of adverse effects or therapeutic failure is essential, particularly when starting a new medication or modifying a treatment regimen.


Collaboration among healthcare professionals is key to preventing medication interactions. Effective communication between physicians, pharmacists, nurses, and other healthcare team members allows for a multidisciplinary approach to patient care. Sharing information on medication lists, allergies, and previous adverse reactions can help identify potential interactions and guide decision-making. Regular medication reviews and follow-

up visits provide opportunities to reassess treatment regimens, discontinue unnecessary medications, and address any concerns or questions patients may have.


Case Studies


The following case studies are hypothetical cases; however, they include OTC products that are commonly used and that may lead to adverse effects in practice.


Case Study 1: Drug Interaction Leading to Adverse Effects




Patient 1, a 65-year-old female, has a history of hypertension and osteoarthritis. She regularly takes prescription medication for her conditions, including amlodipine (a calcium-channel blocker) for blood pressure control and naproxen for pain management. Recently, she developed a cold and decided to self-medicate with an over-the-counter decongestant containing pseudoephedrine.


Patient 1 took the decongestant, pseudoephedrine, and her regular medications, including amlodipine. She was not aware that pseudoephedrine may reduce the antihypertensive effects of amlodipine. Mrs. Johnson experienced an abrupt increase in blood pressure, resulting in symptoms such as dizziness, palpitations, and headache. Concerned about her symptoms, she visited the emergency department, where the interaction between pseudoephedrine and amlodipine was identified as the cause. Patient 1 required immediate intervention, including medication adjustment and close monitoring to stabilize her blood pressure.


Drug-Drug Interaction


Pseudoephedrine is a sympathomimetic agent that has a stimulant effect on the sympathetic nervous system.19 The combination of pseudoephedrine and

a calcium channel blocker such as amlodipine can reduce amlodipine’s efficacy.20,21 This can lead to increased blood pressure and heart rate. An abrupt increase in blood pressure could lead to symptoms such as dizziness, palpitations, and headache.22


Practical Application


Oral pseudoephedrine is an ingredient found in more than 135 OTC and prescription medications.21 Over-the-counter products include Alka-Seltzer Plus Cold Medicine, Liqui-Gels, Aleve Cold and Sinus Caplets, Benadryl Allergy and Sinus Tablets, Claritin-D Non-Drowsy 24-Hour Tablets, just to name a few.21 This hypothetical case highlights the importance of understanding drug interactions, even with seemingly harmless OTC medications. Healthcare professionals must educate patients about potential interactions and encourage them to seek guidance before using new medications, including OTC products. Comprehensive medication reconciliation and patient education can help prevent such incidents and promote safe medication use.


Case Study 2: Drug Interaction Leading to Therapeutic Failure




Patient 2, a 45-year-old male, was diagnosed with depression and started on an antidepressant medication, fluoxetine, by his psychiatrist. Fluoxetine is a selective serotonin reuptake inhibitor (SSRI). Patient 2 was also suffering from chronic insomnia.


Patient 2 began taking an OTC sleep aid containing diphenhydramine without consulting his psychiatrist, not thinking it would interfere with his prescribed antidepressant. After several weeks of taking the sleep aid concurrently with fluoxetine, Patient 2’s family members noticed he was confused, disoriented, and uncharacteristically agitated. Concerned about his deteriorating mental health, they helped him schedule an appointment with his psychiatrist, who identified the drug interaction as the likely cause of Patient 2’s symptoms.

Drug-Drug Interaction


Diphenhydramine is a first-generation antihistamine commonly found in sleep aids.23 Dextromethorphan, and other OTC products like purple echinacea, ginseng, or ginkgo biloba, may increase the concentration of serotonin. If dextromethorphan, or these other products are taken concurrently with an SSRI, e.g., fluoxetine, they may increase the concentration of serotonin to the point where serotonin syndrome occurs.24,25 This is a potentially life-threatening condition.24,25


Practical Application


This case emphasizes the importance of patient education and communication with healthcare providers. Patients should be educated about potential interactions, even with commonly available OTC medications. Proactive engagement between patients and healthcare providers can prevent treatment failures and improve overall treatment outcomes.


Communication Strategies for Counseling Patients on Safe Medication Use


Effective communication between healthcare providers and patients is crucial for counseling on safe medication use. Several communication strategies can enhance patient understanding and adherence to medication regimens. One strategy is using plain language and clear explanations to ensure that patients comprehend the purpose, dosage, and potential side effects of their medications. This approach has been shown to improve medication adherence and reduce adverse events.26 Another strategy is using visual aids, such as medication charts or pictorial instructions, which can enhance patient comprehension and retention of medication instructions.27 Additionally, engaging in active listening and open-ended questioning techniques allows healthcare providers to understand patients better, address misconceptions, and tailor counseling to individual needs.28 The use of teach-back techniques, where patients are asked to explain medication instructions in their own words, can assess patient understanding and identify areas that require further clarification.29 Finally,

fostering a collaborative and non-judgmental environment encourages patients to ask questions, express concerns, and actively participate in decision-making regarding their medication therapy.30


Available Resources for Identifying Drug Interactions


Many OTC products potentially impact the efficacy of prescription drugs or create adverse drug events when two or more drugs are taken together.31 One of the challenges is identifying all the potential drug-drug interactions so they may be avoided or corrected. No regulatory agencies or comprehensive guidelines list or predict the risk of all these interactions. This function should not be left to a clinician’s memory; the potential drug-drug interactions are too expansive. Products that provide interaction details within pharmacy and health system computer systems, textbooks, and journal articles may be used.31


Many healthcare professionals and societies are dedicated to providing information on drug-drug interactions. For example, the International Society for Pharmacoepidemiology has a Drug-Drug Interaction Special Interest Group to inform the base of clinical evidence.32


In addition, databases are being proposed or developed, such as the Center of Excellence for Natural Product Drug Interaction Research, designated by the National Institutes of Health, which provides a framework for modeling pharmacokinetic OTC-drug interactions.33,34 Another is the Drug-Drug Interaction Wide Association Study (DDIWAS).35


Educational institutions like the University of Washington have databases (the University of Washington Drug-Drug Interaction Database) that a clinician could access to help identify potential drug-drug interactions.36 Clinicians need to consider whether the database is generally available or requires a prescription.


Kebodeaux (2019) recommends including patients’ OTC in the patients’ electronic health records.37 This could help identify the OTC drugs a patient is taking. Patients with high-priority health conditions could be specifically

targeted. This approach could include utilizing patient engagement through patient-driven technologies, such as apps, that could be used to update a patient’s digital health records.37




It is crucial for healthcare professionals to be aware of drug metabolism, pharmacokinetics, and pharmacodynamics to identify potential interactions and make informed decisions regarding medication regimens. Drugs may be precipitant drugs if they interfere with another drug’s (the “object” drug’s) absorption, distribution, metabolism, or excretion. It is impractical for a clinician to memorize or know all drug interactions. Staying updated on the latest information in pharmacology and drug interactions is crucial. Continuing education programs, conferences, and professional societies offer valuable platforms for knowledge exchange and discussions on evidence-based practices. Additionally, collaboration among healthcare professionals and the use of electronic resources and medication interaction databases are essential for identifying and preventing potential interactions.


Effective communication in counseling patients on safe medication use can help reduce adverse events. Healthcare providers should speak in plain language. They should use visual aids and active listening techniques to enhance patients’ understanding of their medications and what they do. Healthcare professionals should encourage patients to disclose all medications, including OTC products. Patient education and engagement can then play a vital role in preventing negative medication interactions.


Pharmacy team members are ideally positioned to ensure that consumers understand OTC labels to prevent drug interactions and to place OTCs into the patient record so potential interactions can be evaluated. As more prescription agents receive approval for OTC status, the advisory role regarding possible drug interactions will continue to increase.




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Pirmohamed M, Burnside G, Eriksson N, et al. A randomized trial of genotype-guided dosing of warfarin. N Engl J Med. 2013;369(24):2294- 230

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The information provided in this course is general in nature, and it is solely designed to provide participants with continuing education credit(s). This course and materials are not meant to substitute for the independent, professional judgment of any participant regarding that participant’s professional practice, including but not limited to patient assessment, diagnosis, treatment, and/or health management. Medical and pharmacy practices, rules, and laws vary from state to state, and this course does not cover the laws of each state; therefore, participants must consult the laws of their state as they relate to their professional practice.


Healthcare professionals, including pharmacists and pharmacy technicians, must consult with their employer, healthcare facility, hospital, or other organization, for guidelines, protocols, and procedures they are to follow. The information provided in this course does not replace those guidelines, protocols, and procedures but is for academic purposes only, and this course’s limited purpose is for the completion of continuing education credits.


Participants are advised and acknowledge that information related to medications, their administration, dosing, contraindications, adverse reactions, interactions, warnings, precautions, or accepted uses are constantly changing, and any person taking this course understands that such person must make an independent review of medication information prior to any patient assessment, diagnosis, treatment and/or health management. Any discussion of off-label use of any medication, device, or procedure is informational only, and such uses are not endorsed hereby.


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© RxCe.com LLC 2023: All rights reserved. No reproduction of all or part of any content herein is allowed without the prior, written permission of RxCe.com LLC.