This chapter examines how historical gender biases in medicine have led to significant gaps in healthcare. For decades, medical research predominantly used male subjects, assuming results applied equally to women. This approach has proven flawed—women are underrepresented in clinical trials (just 41% of participants) and sex-specific data are rarely analyzed (reported in under 30% of studies). These oversights have real consequences: women experience more medication side effects, face delayed diagnoses for heart disease due to atypical symptoms, and are more likely to have autoimmune conditions dismissed as psychological. Three key factors are changing this paradigm: scientific evidence showing biological sex differences in drug metabolism and disease presentation; advocacy highlighting systematic exclusion of women from research; and policy reforms requiring gender-inclusive study designs. However, challenges persist. Doctors often misinterpret women’s symptoms—attributing chest pain to anxiety rather than heart disease—while diagnostic patterns reflect gender stereotypes (like overdiagnosing women with borderline personality disorder). Research funding also shows bias, with male-dominated diseases receiving disproportionate resources. The persistence of these gaps demonstrates the need for systemic change. While guidelines now encourage gender-sensitive research, true progress requires transforming medical education, research practices, and clinical decision-making. Only by addressing these biases can medicine achieve accurate diagnoses and effective treatments for all patients.