Medication adherence Research: expert perspectives on key HEOR trends for 2026.

World Adherence Day, observed annually on 27 March, highlights that the availability ofeffective pharmacotherapies alone does not ensure their optimal use in either clinical trialsor real-world practice. Despite decades of evidence demonstrating that suboptimal medication adherence undermines clinical outcomes, potentially leading to avoidable morbidity and mortality and increased healthcare costs, non-adherence remains widespread. At the same time, medication adherence research is evolving rapidly, driven by advances in data infrastructure and analytical methods, technological innovations supporting medication use, and growing attention to health technology assessment (HTA) and implementation considerations. Against the backdrop of World Adherence Day 2026, this editorial aims to provide an overview of these key research trends, viewed through a health economics and outcomes research (HEOR) lens, that are currently shaping themedication adherence field. The intention is to highlight some emerging directions in medication adherence research rather than to prioritise specific trends.