Background <p>Close female friendships provide emotional security and stress buffering, particularly during emerging adulthood, a life stage marked by heightened competition across life domains (e.g. academics; relationships). Yet, these relationships are also uniquely fragile, especially when status differences emerge between friends. The current study examined women’s emotional and physiological responses to imagined performance differences with a close same-sex friend.</p> Methods <p>Eighty-one undergraduate women (<i>M</i>age = 20.15) were randomly assigned to one of three conditions: outperform, equal performance, or underperform relative to a close friend in a self-selected life domain. Emotional responses, anticipated friend reactions, and physiological stress, measured via respiratory sinus arrhythmia (RSA), were recorded. </p> Results <p>As predicted, participants reported the greatest happiness and lowest expectations of negative emotion from their friend in the equal performance condition. RSA decreased significantly during the imagined competition phase, indicating physiological stress, and rebounded during recovery. A marginal interaction between time and hormonal birth control use revealed that naturally cycling women exhibited lower RSA, suggesting higher physiological stress, across all phases compared to those using hormonal contraception. </p> Conclusion <p>These findings suggest that even hypothetical status differences with close friends can elicit measurable stress responses in women. Because ovulation was not directly assessed and hormonal profiles were not measured, interpretations regarding hormonal status should be viewed as preliminary. Results highlight the social and physiological costs of competition in female friendships and offer insight into the evolved trade-offs women navigate between affiliation and status.</p> Clinical Trial Registration <p>Not applicable.</p>