Contents lists available at ScienceDirect International Journal of Psychophysiology journal homepage: www.elsevier.com/locate/ijpsycho Where is the love? A double-blind, randomized study of the effects of intranasal oxytocin on stress regulation and aggression Chelsea Romney a , Jennifer Hahn-Holbrook b , Greg J. Norman c , Andrew Moore d , Julianne Holt-Lunstad e, ⁎ a Department of Psychology, UCLA, United States of America b Department of Psychology, University of California, Merced, United States of America c Department of Psychology, University of Chicago, United States of America d Department of Medicine, University of Utah, United States of America e Department of Psychology, Brigham Young University, United States of America ARTICLE INFO Keywords: Oxytocin Cardiovascular reactivity Aggression Sex difference Hostility Heart rate variability Stress ABSTRACT Previous studies reveal that oxytocin (OT) encourages prosocial behavior in humans; however, animal studies and recent work in humans suggest that OT may also play a role in aggressive behavior and feelings. The present study investigated these competing predictions in the context of a competitive task among 85 healthy human participants (males and females). Using a randomized double-blind design, participants were assigned to an experimental (intranasal OT) or control (intranasal placebo) group. Hostility (Aggression Questionnaire) was measured at home (T1) and in the lab after intranasal administration (T2). Behavioral aggression was assessed post-intranasal administration. There was a significant difference between the OT and the placebo group on hostility scores (p = 0.03) and a significant time by group interaction for behavioral aggression (p < 0.05). Self- reported hostility was significantly higher at T2 compared to T1 (p < 0.001) among participants in the oxytocin group while no significant change was found in hostility among the placebo group. Behavioral aggression was slightly higher in the OT group (compared to the placebo group) directly after OT administration, however, the opposite relationship was found as the study period progressed. Both hostility and behavioral aggression findings were consistent across gender. 1. Introduction Social relationships have a profound influence on health and even longevity (Holt-Lunstad et al., 2010), with isolation and loneliness identified as risk factors for premature mortality (Holt-Lunstad and Smith, 2016; Holt-Lunstad et al., 2015). While the mechanisms ac- counting for this aren't fully understood, there is substantial evidence of multiple psychological, behavioral, and biological pathways (Uchino, 2006). One plausible biological mechanism is oxytocin because it is known for its role in social bonding and stress regulation (Hostinar et al., 2014). Oxytocin (OT) is a neuropeptide and neurotransmitter primarily produced in the hypothalamus (Standring, 2015) and plays a complex role in regulating social behavior and related physiology. In the per- iphery OT receptors are heavily concentrated in the reproductive or- gans and the mammary glands and hence OT is one of the key hormones involved in inducing labor, stimulating milk letdown, and regulating sexual arousal (Gimpl and Fahrenholz, 2001). OT receptors are also expressed in the central nervous system (Gimpl and Fahrenholz, 2001), particularly in parts of the brain associated with social cognition, social motivation, and emotional and threat responses (Loup et al., 1991; Quintana et al., 2017). An extensive body of animal research suggests that across mammalian species endogenous OT facilitates social- bonding by acting on receptors in these aforementioned brain regions to facilitate the process of identifying, remembering, and enjoying the presence of specific individuals (see Bales et al., 2017; Freeman and Young, 2016; Young and Wang, 2004). Exogenous intranasal administration of OT has also been linked to a variety of social behaviors. Experimental manipulations of the OT system have shown that people receiving exogenous doses of intranasal OT are more willing to trust strangers (Kosfeld et al., 2005), identify negative facial expressions more accurately (Di Simplicio et al., 2009), and are primed to remember words with positive valence (Di Simplicio et al., 2009) and novel faces showing positive emotion (Adam J https://doi.org/10.1016/j.ijpsycho.2018.08.010 Received 16 February 2018; Received in revised form 16 August 2018; Accepted 20 August 2018 ⁎ Corresponding author. E-mail address: julianne_holt-lunstad@byu.edu (J. Holt-Lunstad). International Journal of Psychophysiology xxx (xxxx) xxx–xxx 0167-8760/ © 2018 Published by Elsevier B.V. Please cite this article as: Romney, C., International Journal of Psychophysiology, https://doi.org/10.1016/j.ijpsycho.2018.08.010