Multiple medications are often prescribed to help adults with type 2 diabetes manage hyperglycemia, diabetes-associated conditions like hypertension and dyslipidemia, and other comorbidities. “Prior studies have shown that non-adherence to diabetes medications is associated with many adverse outcomes,” says M. Sue Kirkman, MD. Research indicates that better adherence to diabetes medications improves control of intermediate risk factors. It also reduces the likelihood of being hospitalized, can lower healthcare costs, and may decease mortality.

Taking a Closer Look

Studies aiming to estimate rates of adherence to diabetes medications vary widely depending on the types of patients involved in the analysis and how investigators define adherence. Most analyses tend to look at either individual-level or system-level factors independently, but few have used large generalizable cohorts. To address this research gap, Dr. Kirkman and colleagues had a study published in Diabetes Care that used a large national database to look at adherence to oral diabetes medications in more than 200,000 adults with type 2 diabetes in the United States.

For the investigation, the study team used the medication possession ratio, which Dr. Kirkman notes is a fairly standard way to assess adherence. “We pre-specified a number of variables related to patient, provider, and prescription factors, and then looked at their association with adherence,” she says. “A multivariate model was then developed to look at the independent effects of each variable since many of them correlate with one another.”

Important Findings

Overall, about 70% of patients involved in the study were adherent to their medications. “We identified several factors that were associated with non-adherence, including younger age, being new to diabetes therapy, being female, and being on few other medications,” explains Dr. Kirkman (Table 1). Specifically with regard to age, patients aged 25 to 44 were 49% less likely to be adherent when compared with patients aged 45 to 64. Patients between the ages of 65 and 74 were 27% more likely to be adherent, and those aged 75 and older were 41% more likely to be adherent when compared with the 45-to-64 age group. The study team also found that patients who were new to therapy were 61% less likely to adhere to their diabetes medications.

With regard to demographics, men were significantly more likely to adhere to their diabetes drugs than women. Education was also associated with adherence, with patients being more likely to adhere to their medications if they had a higher estimated academic achievement. Patients who completed graduate school were 41% more likely to be adherent than those with a high school equivalent education. Patients with an annual income that topped $60,000 were also more likely to be adherent when compared with those making less than $30,000. Little variation was seen across geographic regions, but patients living in the Midwest were 12% more likely to be adherent than those in the West.

Other Key Factors

“Non-adherence was also associated with higher out-of-pocket costs and use of retail pharmacies versus mail order pharmacies,” says Dr. Kirkman. Patients using mail order pharmacies were more than twice as likely to be adherent to their medications when compared with those who filled their prescriptions at retail pharmacies (Table 2). Total daily pill burden was also an adherence factor. For each additional pill that patients took per day, adherence to antidiabetic drugs increased by 22%. The authors also found that diabetes medication adherence decreased by 11% for each additional $15 that was spent in out-of-pocket costs per month.

Several prescriber factors were also examined in the analysis. No significant differences were seen in patient adherence by sex of the prescriber and the effect size of prescriber age was very small. In addition, no significant differences in adherence were observed between primary care and endocrinologist prescribers. However, patients with non-endocrinologist specialists who were their prescribers had slightly but significantly lower adherence than those with primary care prescribers.

Examining the Implications

“More research is needed to gain a better understanding about why being new to diabetes therapy or being on fewer medications overall was associated with lower adherence in our study,” Dr. Kirkman says. “We can only speculate on the potential rationale behind this, but it’s possible that that these patients may not view themselves as truly being ‘ill’ and may be less likely to take medications, especially when the disease is asymptomatic. Regarding patient age as a factor, it’s possible that older patients have more comorbidities and are used to taking medications regularly. Their daily routine might make them more likely to adhere to their diabetes medications.”

Dr. Kirkman says findings of the study are helpful to healthcare providers in raising awareness of both modifiable and non-modifiable factors that are associated with lower adherence. “Clinicians need to be aware of these factors and target programs or interventions to improve adherence,” she says. “Healthcare providers and system leaders should work together to target potentially modifiable factors, such as getting more patients to use mail order pharmacies and doing more to lower patients’ out of pocket costs.”