This study examined the relationship between medication adherence and future healthcare costs using pharmacy claims data. It found that increased medication adherence, as measured by compliance and persistence, was associated with lower total future healthcare costs. The study also found that using a boosted regression model that incorporated medication adherence measures provided similar or better predictive accuracy for future healthcare costs compared to other econometric models. However, overfitting was an issue with the boosted regression model that would need to be addressed through parameter respecification.