Steven E. Meredith and Nancy M. Petry
Increasing the effectiveness of adherence interventions may have a far greater impact on the health of the population than any improvement in specific medical treatments.
—R. Brian Haynes (2001)
Introduction
Nearly half of all Americans take at least one prescription medication (Centers for Disease Control and Prevention, 2015), and this proportion is expected to increase as the US population ages. Although medications have been used to improve the health and wellbeing of millions of individuals around the world, drugs only work for patients who take them. Nonadherence leads to poor health outcomes, increased mortality, disease spread, and avoidable health care costs, including $100 billion annually in excess hospitalizations (Osterberg and Blaschke, 2005).
Some estimates suggest as many as 28 percent of new prescriptions in the US are never filled (Fischer et al., 2010), and for patients who fill their prescriptions, nonadherence may still become a problem even after they leave the pharmacy. Patients must then take the correct number of doses at the appropriate interval and refill their prescriptions as often and for as long as their health condition requires. Thus, for any given patient, the rate of
medication adherence can vary widely from 0 percent to over 100 percent (if the patient takes more than the amount prescribed).
Although taking too much medication is problematic, patients typically do not take enough. Rates of medication adherence must be relatively high for patients to reap the full therapeutic benefits of prescription drugs. For instance, in a study that was conducted prior to recent advances in antiretroviral therapy, Paterson et al. (2000) found patients who were prescribed protease inhibitors for HIV needed to achieve adherence rates of 95 percent or higher to suppress viral replication. Regardless of the disease or drug, however, patients are generally considered adherent if they take at least 80 percent of their medication, and for many drugs, this level of adherence can produce significant health benefits (e.g., Wei et al., 2002).
Although most patients are unlikely to achieve optimal levels of medication adherence, estimating the average rate of adherence among all patients is challenging because rates vary by medication and participant characteristics. Further, measures of adherence are inconsistent across studies (e.g., self-report, pill count, or pharmacy claims data). Nevertheless, most research suggests many patients stop taking medications within a few months after filling their first prescription, and average rates of adherence typically range from 50 to 75 percent (Cramer and Rosenheck, 1998; DiMatteo, 2004;
Osterberg and Blaschke, 2005).
Medication adherence and chronic disease
Medication adherence is critically important to treating all types of medical problems, including acute health conditions such as those requiring antibiotics. However, adherence is often lowest among patients with chronic diseases. Recent estimates indicate about half of US adults suffer from at least one chronic disease (Ward et al., 2014), and a 2003 report by the World Health Organization suggests adherence to therapies for chronic diseases is roughly 50 percent in developed countries and even lower in developing countries (Sabaté, 2003).
For patients with chronic health conditions, research shows poor medication adherence leads to increased service utilization, diagnostic testing, treatment for comorbid conditions, hospitalization, and, consequently, higher health care costs. For example, in a population-based
sample of over 137,000 patients, Sokol and colleagues (2005) found significantly higher hospitalization rates in nonadherent patients with diabetes, hypertension, congestive heart failure, and high cholesterol relative to adherent patients with the same chronic health conditions. In addition, they found disease-related health care costs were significantly higher among nonadherent patients who had diabetes and high cholesterol relative to adherent patients with the same conditions.
To make matters worse, poor adherence among patients with chronic diseases is also associated with increased mortality (Simpson et al., 2006).
For example, in a study of patients with heart disease and diabetes, Ho and colleagues found patients who were nonadherent to their cardioprotective medication (e.g., angiotensin-converting enzyme inhibitors and statins) had a significantly higher rate of mortality than adherent patients (12.1% vs. 6.7%;
Ho et al., 2006).
Barriers to medication adherence
The problem of nonadherence is widespread and has been attributed to a variety of factors (Brown and Bussell, 2011). According to a survey of nearly 10,000 US patients, the most commonly reported reasons for missing a dose of medication are forgetting to take the medication, avoiding (real or perceived) side effects, the high cost of the medication, and believing the medication will have little or no effect on health (Boston Consulting Group, 2003). Table 7.1 lists some of the most common barriers to medication adherence.
TABLE 7.1 Barriers to medication adherence Patient Level Financial Low income
No health insurance
Lack of transportation to medical appointments or pharmacy Mental/cognitive Forgetting to take medication
Poor health literacy Cognitive impairment
Substance abuse
Serious psychiatric illness Negative beliefs/
attitudes Lack of faith in treatment effectiveness Belief that an asymptomatic disease
does not require treatment
Misinformation about medication or disease
Medication/
Provider Level Financial High drug costs High copayments
Other Negative side-effects of medication Multiple or complex medication
regimens
Lack of follow-up
Lack of patient education
Importantly, many barriers to adherence are surmountable, and researchers, practitioners, and policymakers have developed and tested various interventions designed to help patients overcome these barriers. The remainder of this chapter will review some of these medication adherence interventions, with a special focus on reinforcement-based behavioral economics interventions.