Weighing the Impacts of GLP-1s: Quasi-Experimental Evidence From Provider Adoption

The arrival of GLP-1 medications has been described as one of the most important health care innovations in recent years. We provide large-scale quasi-experimental evidence on their real-world impacts by exploiting variation in the eventual prescribing propensities of patients’ pre-existing primary care providers. Using a panel intent-to-treat design, we compare outcomes for 1.4 million diabetic or obese veterans based on their 2018 provider’s eventual propensity to adopt GLP-1s, leveraging comprehensive electronic health records and biomarker data from the Veterans Health Administration, a setting with minimal insurance attrition and low-cost access to these drugs. Patients whose providers become higher propensity adopters experience substantial improvements in glycemic control and clinically meaningful weight loss; our treatment-on-the-treated estimates closely match estimates from clinical trials. Despite these metabolic benefits, we find no statistically significant average effects on emergency department utilization, mental health and substance use outcomes, or non–GLP-1 medical spending through 2024. However, quantile regression results show heterogeneous effects, with spending declining at lower quantiles and rising at higher quantiles for patients of higher-propensity adopters.