RESEARCH REPORT Intranasal Oxytocin Increases Positive Communication and Reduces Cortisol Levels During Couple Conflict Beate Ditzen, Marcel Schaer, Barbara Gabriel, Guy Bodenmann, Ulrike Ehlert, and Markus Heinrichs Background: In nonhuman mammals, the neuropeptide oxytocin has repeatedly been shown to increase social approach behavior and pair bonding. In particular, central nervous oxytocin reduces behavioral and neuroendocrine responses to social stress and is suggested to mediate the rewarding aspects of attachment in highly social species. However, to date there have been no studies investigating the effects of central oxytocin mechanisms on behavior and physiology in human couple interaction. Methods: In a double-blind placebo-controlled design, 47 heterosexual couples (total n = 94) received oxytocin or placebo intranasally before a standard instructed couple conflict discussion in the laboratory. The conflict session was videotaped and coded for verbal and nonverbal interaction behavior (e.g., eye contact, nonverbal positive behavior, and self-disclosure). Salivary cortisol was repeatedly mea- sured during the experiment. Results: Oxytocin significantly increased positive communication behavior in relation to negative behavior during the couple conflict discussion (F = 4.18, p = .047) and significantly reduced salivary cortisol levels after the conflict compared with placebo (F = 7.14, p = .011). Conclusions: These results are in line with animal studies indicating that central oxytocin facilitates approach and pair bonding behavior. Our findings imply an involvement of oxytocin in couple interaction and close relationships in humans. Key Words: Couple conflict, intranasal oxytocin, salivary cortisol, social interaction, stress C lose social relationships play a key role for wellbeing and longevity in humans (1–3). It has been suggested that this beneficial effect of social relationships and particularly of positive couple interaction is mediated through a reduced reac- tivity of physiological stress systems, namely the hypothalamic- pituitary-adrenal (HPA) axis and the autonomous nervous system (ANS) (4–6). Conversely, marital discord and specifically hostile behavior during couple conflict in unhappy relationships have been shown to substantially impair psychological and physiolog- ical well-being (7–9). To date, it is unclear which neurophysio- logical mechanisms mediate both the beneficial effects of happy close social relationships on psychobiological stress systems as well as the negative effects of repeated and intense couple conflict. A large body of evidence links the central activity of the neuropeptide oxytocin with affiliative behavior as well as with stress reduction in nonhuman mammals (10,11). In line with this research, initial studies suggest similar social and stress-reducing effects of oxytocin in humans. Notably, recent neuropharmaco- logical research has shown that neuropeptides gain access to the human brain after intranasal administration (12), providing a useful method for studying the central nervous effects of oxyto- cin in humans (13). Intranasal oxytocin was found to reduce endocrine and psychological responses to social stress (14), to modulate social memory (15,16), and to increase trust and eye-gazing (17,18) and the ability to infer the mental state of another person (“mind-reading”) (19). In line with this, the hormone was shown to attenuate amygdala responses to emo- tional faces (20,21) and during prosocial behavior (22). The effects of intranasal oxytocin in human couple interaction have not been investigated so far. Given that oxytocin seems to promote pair bonding behavior in nonhuman mammals and social approach behavior in humans, we hypothesized that oxytocin might affect communication and stress responsiveness in human couples. In this study, we investigated the effects of a single dose of intranasal oxytocin in comparison with placebo on interaction behavior and HPA axis activity during a laboratory couple conflict discussion. Methods and Materials Forty-seven heterosexual couples (n = 94 subjects), aged 20 –50 years, who were married or had been cohabiting for at least 1 year participated in the study. Exclusion criteria for participation were smoking, chronic mental or physical illness, medication intake and, for women, the intake of hormonal contra- ceptives, current pregnancy, and breastfeeding. All women were investigated during the luteal phase of their menstrual cycle. Sub- jects were informed that we were interested in hormonal influences on couple communication and that they would receive either oxytocin or placebo before a conflict conversation in the labo- ratory. All couples gave written informed consent and were offered 100 Swiss Francs for participation. The study was ap- proved by the ethics committee of the University of Zurich and the Canton of Zurich. To assess equivalence among oxytocin and placebo groups, the General Health Questionnaire (GHQ) (23), the Relationship Questionnaire (PFB) (24), and the Short Chronic Stress Scale (SSCS) (25) were analyzed in all subjects before participation in the study. Experiments took place in the laboratories of the Department of Psychology at the University of Zurich between 5:00 PM and 7:30 PM to control for diurnal variation in salivary From the Department of Psychology (BD, UE), Clinical Psychology and Psy- chotherapy; Department of Psychology, Clinical Psychology and Psy- chobiology (MH), University of Zurich, Zurich; Department of Psychol- ogy (MS, BG, GB), Institute for Family Research and Counseling, University of Fribourg, Fribourg, Switzerland; and the Department of Psychiatry and Behavioral Sciences (BD), Emory University School of Medicine, Atlanta, Georgia. Address reprint requests to Beate Ditzen, Ph.D., University of Zurich, Depart- ment of Psychology, Clinical Psychology and Psychotherapy, Binzmu- hlestr. 14/Box 26, CH-8050 Zurich, Switzerland; E-mail: b.ditzen@ psychologie.uzh.ch. Received June 13, 2008; revised October 8, 2008; accepted October 8, 2008. BIOL PSYCHIATRY 2009;65:728 –731 0006-3223/09/$36.00 doi:10.1016/j.biopsych.2008.10.011 © 2009 Society of Biological Psychiatry