Binary sex studies in biomedical research have been criticized as overly simplistic, but abandoning them would hinder progress in a long-neglected area of biomedicine. Historically, female animals and women have been excluded from biomedical research, but the NIH Revitalization Act of 1993 mandated the inclusion of women and under-represented groups in clinical trials. By 2009, over 60% of human studies included both sexes, while only 26% of non-human studies did. In 2016, the NIH implemented guidelines requiring the inclusion of sex as a biological variable in preclinical research, leading to a 49% increase in studies using both sexes by 2019. The inclusion of female participants and animal subjects is already having a revolutionary impact on areas such as chronic pain, mental health, and immune function. However, there is a growing threat from those who misuse research on sex differences to marginalize individuals or reinforce stereotypes. The authors argue that comparing female and male individuals in biomedical research remains essential for understanding biological differences and their impact on health. They acknowledge concerns about gendered environments and non-sex-related variables, but emphasize that sex is a valid biological concept. Research on sex differences has revealed important insights into immune function, pain, and mental health. For example, female mice often have stronger immune responses, and sex chromosomes play a role in various physiological and behavioral traits. Studies on pain have shown that different mechanisms are involved in males and females, and that testosterone levels influence these differences. The authors conclude that comparing female and male individuals is crucial for advancing biomedical research and improving human health. They support efforts to investigate both biological and social determinants of disease, and urge continued research on sex differences.Binary sex studies in biomedical research have been criticized as overly simplistic, but abandoning them would hinder progress in a long-neglected area of biomedicine. Historically, female animals and women have been excluded from biomedical research, but the NIH Revitalization Act of 1993 mandated the inclusion of women and under-represented groups in clinical trials. By 2009, over 60% of human studies included both sexes, while only 26% of non-human studies did. In 2016, the NIH implemented guidelines requiring the inclusion of sex as a biological variable in preclinical research, leading to a 49% increase in studies using both sexes by 2019. The inclusion of female participants and animal subjects is already having a revolutionary impact on areas such as chronic pain, mental health, and immune function. However, there is a growing threat from those who misuse research on sex differences to marginalize individuals or reinforce stereotypes. The authors argue that comparing female and male individuals in biomedical research remains essential for understanding biological differences and their impact on health. They acknowledge concerns about gendered environments and non-sex-related variables, but emphasize that sex is a valid biological concept. Research on sex differences has revealed important insights into immune function, pain, and mental health. For example, female mice often have stronger immune responses, and sex chromosomes play a role in various physiological and behavioral traits. Studies on pain have shown that different mechanisms are involved in males and females, and that testosterone levels influence these differences. The authors conclude that comparing female and male individuals is crucial for advancing biomedical research and improving human health. They support efforts to investigate both biological and social determinants of disease, and urge continued research on sex differences.