Abstract: The invention provides a method of treating a psychiatric or medical disorder in a mammalian subject, the method comprising administering to the subject an effective amount of an oxytocin receptor agonist (e.g., oxytocin). Optionally, the oxytocin receptor agonist is delivered by intranasal administration. Further provided is a method of increasing social cognition, increasing social functioning, increasing empathy, increasing trust of others, reducing paranoia and/or reducing hostility in a subject with a psychotic disorder, a mood disorder characterized by psychotic features, a personality disorder or a pervasive developmental disorder, the method comprising administering to the subject an effective amount of an oxytocin receptor agonist.