Twenty years of sex and gender science in health research: a policy statement from the Organization for the Study of Sex Differences.

Sex and gender are fundamental determinants of health, disease risk, and treatment responses, yet they remain inconsistently and inadequately integrated into biomedical research. Despite major funding and regulatory policies over the past two decades, sex and gender continue to be treated primarily as descriptive variables rather than drivers of discovery. As the Organization for the Study of Sex Differences (OSSD) marks twenty years of leadership in this field, this policy statement articulates OSSD's position on best practices for the integration of sex and gender in health research. Drawing on empirical evidence, landmark policies, and persistent gaps in implementation, this statement provides clear guidance for researchers, funders, and journals. OSSD explicitly recommends prespecified sex- and gender-responsive questions, appropriate study design and statistical power, transparent analysis and reporting, and accountability mechanisms to translate into practice. Adoption of these standards is essential to improving scientific rigor, reproducibility, and clinical relevance.