Over 700,000 adverse drug events (ADEs) result in emergency hospital visits annually, and many of these ADEs are preventable through the use of health information technology in hospitals. However, only 12.6% of U.S. hospitals have developed the capacity to adopt closed-loop electronic medical records (EMR). Organizational complexity may be a major factor influencing hospitals' adoption of closed-loop EMR. This quantitative study explored how organizational complexity influenced hospitals' adoption of closed-loop EMR. Diffusion of innovation theory was the foundation for this study. Logistic regression was used to establish possible relationships between organizational complexity and hospitals' adoption of EMR for closed-loop medication therapy management. Secondary data from Health Information and Management Systems Society were examined to explore the relationship between organization complexity and hospitals' adoption of EMR for closed-loop medication therapy. The research questions explored whether vendor selection strategy, structural complexity, and management structure influence hospitals' adoption of EMR for closed-loop medication therapy management. The results indicated that all three variables, vendor selection strategy, structural complexity, and management structure, are statistically significant predictors of hospitals' adoption of EMR for closed-loop medication therapy management. Results from this study may promote positive social change by enhancing hospitals' adoption of EMR for closed-loop medication therapy management, which may therefore help improve the quality, efficiency, and safety of health care delivery in U.S. hospitals.