Global Inequalities in Clinical Trials Participation

Clinical trials are fundamental to the production of medical evidence and determine who gains access to experimental therapies. Although prior work has long documented inequalities in global clinical trial participation, a systematic quantification of the relative contributions of country-level factors and disease burden remains absent. This paper analyzes inequality in participation across 78,117 randomized controlled trials (RCTs) spanning 16 major disease categories from 2000 to 2024. Linking 185.6 million RCTs participants to country-level disease burden, the paper shows that inequalities in RCTs participation are predominantly explained by country-level factors rather than disease burden. Country-level factors account for 88.9% of the variation in participation, whereas disease and temporal effects contribute marginally. Removing entire disease categories, including those traditionally underfunded, has little effect on overall inequality. Instead, participation is highly concentrated geographically, with a small group of Global North countries enrolling a disproportionate share of participants across nearly all diseases. These patterns persist despite decades of disease-targeted funding and increasing alignment between research efforts and disease burden. Findings also show that without parallel horizontal investments in research capacity, health infrastructure, and governance, even well-funded disease programs are insufficient to reduce inequality in clinical trial participation.