Work disability evaluation plays a central role in medical certification in sickness benefit schemes. This guides effective decision making for return-to-work timelines. Countries that incorporate it have varied approaches. To improve fairness and consistency, Sweden adopted disease-specific guidelines, particularly for complex health conditions such as mental disorders, cancer, and neurological diseases, whereas in the United Kingdom, a fit note system highlights the ease of fitness-for-work assessments in clinical settings. For a successful implementation of the sickness benefit scheme in Korea, it is essential to review international acumen in work disability evaluation and medical certification. This study also examines challenges that physicians face in certification, factors influencing assessments, and the usefulness of disease-specific guidelines. In many countries, administrative burdens, uncertainty in diagnosis, and ethical conflicts complicate physicians' tasks. Countries such as Sweden, France, and Ireland, have addressed these issues by developing structured certification tools and support systems. Learnings from the recent Korean pilot programs, this review identifies the following core priorities: developing disease-specific guidelines, providing clinical support for physicians’ decisions, and integrating occupational health expertise. These guidelines should function not only as administrative checklists, but also as potential clinical tools that consider both patient functionality and job characteristics. Finally, this study offers policy and practical insights to help design a consistent and fair medical certification system for Korea’s sickness benefit program that encourages timely medical intervention, prevents presenteeism, and promotes sustainable workforce reintegration.