Scope-of-Practice for Nurse Practitioners and Adherence to Medications for Chronic Illness in Primary Care



Nonadherence to medications is costly and improving adherence is difficult, requiring multifactorial solutions, including policy solutions.


The purpose of this study is to evaluate the effect of one policy strategy on medication adherence. Specifically, we examine the effect on adherence of expanding scope-of-practice regulations for nurse practitioners (NPs) to practice and prescribe without physician supervision.


We conducted three difference-in-difference multivariable analyses of commercial insurance claims.


Patients who filled at least two prescriptions in one of three chronic therapeutic medications: anti-diabetics (n = 514,255), renin angiotensin system antagonists (RASA) (n = 1,679,957), and anti-lipidemics (n = 1,613,692).

Main Measures

Medication adherence was measured as the proportion of days covered (PDC). We used one continuous (PDC 0–1) and one binary outcome (PDC of > .8), the latter indicating good adherence.

Key Results

Patients taking anti-diabetic medications had a 1.9 percentage point higher medication adherence rate (p < 0.05) and a 2.7 percentage point higher probability of good adherence (p < 0.001) in states that expanded NP scope-of-practice. Medication adherence for patients taking RASA was higher by 2.3 percentage points (p < 0.001) and 3.4 percentage points (p < 0.01) for both measures, respectively. Patients taking anti-lipidemics saw a smaller, but statistically insignificant, improvement in adherence.


Results indicate that scope-of-practice regulations that allow NPs to practice and prescribe without physician oversight are associated with improved medication adherence. We postulate that the mechanism for this effect is increased access to health care services, which in turn increases access to prescriptions. Our results suggest that policies allowing NPs to maximally use their skills can be beneficial to patients.

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This study was in part funded by the Laura and John Arnold Foundation through a grant from the Health Care Cost Institute and National Academy for State Health Policy.

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Correspondence to Ulrike Muench PhD RN.

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Muench, U., Whaley, C., Coffman, J. et al. Scope-of-Practice for Nurse Practitioners and Adherence to Medications for Chronic Illness in Primary Care. J GEN INTERN MED (2020).

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  • medication adherence
  • nurse practitioners
  • scope-of-practice
  • policy evaluation
  • administrative claims data