Just What the Nurse Practitioner Ordered: Independent Prescriptive Authority and Population Mental Health

Limited access to mental health care services in the United States is a major public health concern. While one in five Americans suffers from a mental illness, a nearly equal proportion of the population lives in areas that are underserved by mental health care providers. As mental health problems tend to develop early in life and persist over the lifecycle, the costs of not receiving treatment can be devastating. In addition to direct medical costs, untreated mental illnesses are associated with lower human capital accumulation, worse labor market participation and performance, and greater criminal activity (e.g., Currie and Stabile [2006], Ettner et al. [1997], and Greenberg and Rosenheck [2008]).

In this paper, we examine whether allowing nurse practitioners (NPs) to prescribe medication without physician supervision or collaboration is associated with improved mental health outcomes. We make two key contributions to our understanding of the effects of scope of practice legislation on access to care and population health. First, we show that states that broaden prescriptive authority see both improvements in self-reported mental health and decreases in the number of mental-health-related deaths, including suicides. These benefits are more pronounced among those with less education, and among populations in areas with fewer psychiatrists per capita. Second, we show that independent prescriptive authority for NPs is not associated with a crowding out of physicians provided services. Together, our results suggest that granting independent prescriptive authority to NPs is an important policy tool that may be used to improve health outcomes for populations that have limited access to care.

We exploit within-state variation in scope of practice legislation from 1990 to 2014 to examine how both population mental health and prescribing behaviors of physicians change when NPs are granted independent prescriptive authority. We find that mental health outcomes improve when a state allows NPs to independently prescribe, while the number of prescriptions written by physicians for antidepressants and antipsychotics are unaffected. On average, granting NPs independent prescriptive authority is associated with a reduction of 4% in days of poor mental health, and a reduction of 12% in mental-health-related deaths.

These improvements in mental health outcomes are more pronounced in areas underserved by psychiatrists and among already disadvantaged populations. In particular, areas that are underserved by psychiatrists see improvements in self-reported mental health and mental-health-related mortality that are 40% and 200% greater than those observed in areas with a sufficient provision of psychiatrists, respectively. Populations with low levels of education see improvements that are even greater: the average low-education resident in a state with fewer psychiatrists per capita sees improvements that are 70% greater than the average resident in a state that is better equipped for mental health care.

The potential for legislative action remains large: as of January, 2015, only 24 states and the District of Columbia had granted independent prescriptive authority to NPs. Our results indicate that liberalizing scope of practice legislation for non-physician providers can help mitigate the impacts of limited access to physician-provided health care.