Kimberly Finley, PharmD, BCACP

Despite major advancements in health care, the simple concept of adherence to a prescribed medication regimen is often overlooked in the health care system. Carolyn Clancy, MD, former director of the Agency for Healthcare Research and Quality, said “medication adherence is America’s new drug problem.”

Medication nonadherence results in upwards of 100,000 deaths per year and billions in health care spending annually.

 Whether it is a newly discovered medication or a tried-and-true remedy of the past, a medication only works when it is taken correctly.

Medication adherence is essential for each medication to have its therapeutic effect in every patient. Interventions to improve medication adherence may have a greater impact on individual patients and the population as a whole than any novel treatment or therapy.

 To address nonadherence and remove the potential barrier of accessibility to medications, 90-day supplies are commonly offered as a solution.

By looking deeper into what medication adherence is, how it is measured, and meaningful ways to address the barriers that patients experience, providers must stop and reconsider the role that 90-day supplies have in addressing medication nonadherence.

On paper, medication adherence may seem straightforward. But add in human beings and their fallibility and medication adherence can become a lot more complicated.

The definition of medication adherence and how it is measured can vary widely depending on the source. At a basic level, medication adherence is defined as the extent to which a patient adheres to the prescribed dose and interval of their medication regimen.

A patient’s thoughts, beliefs, attitudes, lifestyle, socioeconomic status, stress level, chronic disease states, medications, and many other factors influence how a patient interacts with the health care system and subsequently how adherent a patient is to their medication regimen. Data surrounding medication adherence and associated patient behavior stem from assessing medication use in patients with chronic diseases.

The CDC states that 6 in 10 US adults have at least one chronic disease state and 4 in 10 US adults have two or more chronic disease states.

 It is also estimated that patients are nonadherent to their medications at least 50% of the time, with nonadherence rates reaching as high as 80% in asymptomatic conditions, such as hypertension.

Although widely discussed and researched, medication nonadherence is often an insidious issue that goes unnoticed or unaddressed in many health care settings. To address medication adherence, different approaches have been developed to objectively define and measure adherence.

Proportion of Days Covered (PDC) and 90-Day Supplies

In 2007, the Centers for Medicare & Medicaid Services (CMS) created a star rating system to inform beneficiaries of a Medicare Advantage plan’s performance and to encourage continued quality improvement at the plan level.

 In the star rating system, medication adherence is measured for oral antidiabetic medications, antihypertensive medications (renin-angiotensin system antagonists), and statins.

To measure medication adherence, CMS adopted the Proportion of Days Covered (PDC) approach (

). PDC was developed by Pharmacy Quality Alliance (PQA) in 2002 and provides a measurement by using pharmacy claims data and comparing the number of days the patient is covered with the medication to the number of days in that period.

A higher PDC rate indicates better adherence with 0.8 or higher representing adherence to a medication.

 The PDC approach—and other measurements from pharmacy claims data—assumes perfect medication-taking behavior as long as the patient has access to the medication.

Since the adoption of the PDC approach by CMS, many other insurance companies have followed suit. When a medication is filled as a 90-day supply, many benefits are offered, including cost-savings to the pharmacy and insurance plan, improved adherence as measured by PDC, and increased convenience for the patient due to fewer trips to the pharmacy.

Access to 90-day supplies began to expand as payers and pharmacy benefit managers (PBMs) started to enhance their retail pharmacy networks and pharmacy benefit designs.

 The amount of 90-day prescriptions dispensed by retail pharmacies has continued to increase, from fewer than 7% of retail prescriptions in 2010 to nearly 20% in 2019.

Unfortunately, the push for 90-day supplies is driven by PDC data, which is an objective measure of adherence that only reveals one piece of the patient’s true medication-taking behavior. According to PQA, PDC is not a measure that is intended for clinical decision-making or guiding individual patient-care decisions, but rather a retrospective, population-level assessment.

Switching to a 90-day supply has become a popular approach to increase medication adherence, but is this really the best option for patients? On one hand, 90-day supplies contribute to increased cost-savings and open the door to possible reimbursement, allowing health care providers to continue providing high-quality service to patients.

On the other hand, 90-day supplies will ultimately lead to less patient interaction with the health care system and may allow poor medication-taking behaviors to continue. Unfortunately, a 90-day supply is not a one-size-fits-all approach to improving medication adherence.

For example, if a patient is filling their medication every 90 days, pharmacist interaction may decrease from 12 to 4 times per year. As the most accessible health care practitioner, pharmacists provide a wealth of knowledge to help patients manage their chronic disease states, understand their medications, and simplify complex regimens.

Patients who are struggling to overcome adherence barriers are slipping through the cracks of the health care system and the cycle of nonadherence, poor disease state management, and overutilization of the health care system continues (

There is no gold standard to accurately measure medication adherence. Direct measurements, such as body fluid assays of the drug and its metabolite or direct observation of drug administration, are applicable but not realistic for most clinical practice.

Indirect measurements, such as medication adherence scales, are a subjective measurement of adherence that rely solely on self-reporting by the patient. Pill counts and pharmacy claims data are indirect, objective measurements of medication adherence that function under the often incorrect assumption that as long as the patient has the medication in their possession, they are taking it correctly.

A patient-provider relationship based on trust and communication, patient understanding of the health care system, and social support are all vital components of medication adherence that are not captured in traditional approaches to medication adherence measurement.

 Providers should consider how medication adherence is assessed for their patients to determine an approach that best fits their patient population.

A combination of direct and indirect adherence measurements, as well as simply getting to know a patient on a personal level rather than only looking at pharmacy claims data, will allow a more accurate view of a patient’s adherence.

As medication adherence is complex, solutions addressing this issue are also multi-faceted and patient specific. Meaningful solutions to barriers of medication adherence take time and require investment from the patient and health care providers involved in their care.

Although many providers believe that nonadherence stems from forgetfulness or lack of access to medications, nonadherence often has more to do with a conscious choice made by the patient.

 One of the first steps when addressing medication adherence is to assume nonadherence, not as a way to reprimand patients, but to create room for an open and honest conversation.

Using open-ended questions that require more than a simple yes or no response when asking about medication adherence helps to create a blame-free, non-judgmental environment. If a patient confides in their health care provider about nonadherence or issues they are having with their medication regimen, it is important to thank them for being forthcoming and sharing that information.

It is crucial that patients see their health care practitioners not only as highly competent, but also as having genuine care and compassion for them and their health care.

 Although trust takes time to build, it is foundational in how patients interact with the health care system and participate in their own health care.

Efforts to provide consistent and continual patient education and encouraging use of medication adherence aids (medication calendar, pill box, etc.) are also essential components in addressing medication adherence. Although switching patients to a 90-day supply of their medicine may be more convenient and may even result in an incentive or reimbursement, providers should consider if it will address the true barriers to adherence that the patient is facing.

There are many other ways for health care practitioners to not only address nonadherence but to make a significant and lasting impact on their patients and the way they take their medications.

Health care is everchanging with new medications, new treatment algorithms, and new technologies to diagnose and treat patients. The complexities of the health care system can be confusing and difficult to navigate for many patients.

A health care provider who invests an extra moment of time to make a personal connection with their patients can make all the difference in their health care journey. Nonadherence is a multi-faceted and complex issue that is all too often overlooked and given a simple solution of a 90-day supply.

To truly address the barriers to medication adherence, it requires a multitude of factors and interventions from the patient and health care provider. Poor medication taking behavior and low PDC rates often require a personalized intervention that goes beyond the convenience offered by a 90-day supply. 

Efforts aimed at improving medication adherence should not be overlooked and may be one of the most impactful interventions a health care provider can make for their patients.

PGY2 Ambulatory Care Pharmacy Resident, AdventHealth Celebration, Celebration, FL.

Clinical Pharmacist, AdventHealth Celebration, Celebration, FL.

Julia Nickerson-Troy, PharmD, MS, BCACP, 

Director, PGY1 and PGY2 Ambulatory Care Pharmacy Residency Program, AdventHealth Celebration, Celebration, FL.

Conceptualization (BSS), Resources (BSS), Supervision (All), Writing – original draft (BSS), Writing – review & editing (All).

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

The authors declare no relevant conflicts of interest or financial relationships.

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Interventions to improve medication adherence may have a greater impact on individual patients and the population as a whole than any novel treatment or therapy.