[Oxytocin versus dopamine: The delicate balance between social bonding and addiction]

Social behaviour is fundamental to survival and adaptation, relying on complex, interacting neurobiological systems in which the neuropeptide oxytocin (OT) and the neurotransmitter dopamine (DA) play pivotal roles in regulating social bonding, motivation, and reward processing. This review synthesises recent advances in understanding the bidirectional interactions between OT and DA within key nodes of the brain's reward circuitry, including the nucleus accumbens, ventral tegmental area, amygdala, and medial prefrontal cortex. We examine how these interactions support a wide range of social behaviours in humans and animals, from reproductive bonds such as pair bonding and parental care to non-reproductive interactions like social exploration, cooperation, and aggression. A central focus is the disruptive impact of psychostimulants (e.g., cocaine, amphetamines) on OT-DA balance in rodents. These substances alter DA signalling, shifting reward valuation and reducing the prioritisation of natural social rewards while increasing the drive for psychostimulant-seeking behaviour. This imbalance impairs social motivation and bonding. Importantly, positive social interactions can serve as competing natural rewards that prevent, and in some cases reverse, psychostimulant-seeking behaviours, highlighting the therapeutic potential of targeting OT-DA pathways. By integrating findings from animal models and human studies, this review proposes a framework for understanding how the brain arbitrates between social and pharmacological rewards, and how this balance is modulated by internal states, environmental factors, and the pathological effects of addictive substances.