We investigated the effects of intranasal oxytocin (OXT) on trust and cooperation in borderline personality disorder (BPD), a disorder marked by interpersonal instability and difficulties with cooperation. Although studies in healthy adults show that intranasal OXT increases trust, individuals with BPD may show an altered response to exogenous OXT because the effects of OXT on trust and pro-social behavior may vary depending on the relationship representations and expectations people possess and/or altered OXT system functioning in BPD. BPD and control participants received intranasal OXT and played a social dilemma game with a partner. Results showed that OXT produced divergent effects in BPD participants, decreasing trust and the likelihood of cooperative responses. Additional analyses focusing on individual differences in attachment anxiety and avoidance across BPD and control participants indicate that these divergent effects were driven by the anxiously attached, rejection-sensitive participants. These data suggest that OXT does not uniformly facilitate trust and pro-social behavior in humans; indeed, OXT may impede trust and pro-social behavior depending on chronic interpersonal insecurities, and/or possible neurochemical differences in the OXT system. Although popularly dubbed the 'hormone of love', these data suggest a more circumspect answer to the question of who will benefit from OXT.