The core symptoms of autism spectrum disorder (ASD) comprise impairments of social communication and social interactions as well as restricted and repetitive patterns of interests and activities. No definitive treatments for these core symptoms currently exist. Oxytocin, a highly conserved peptide, has been suggested to moderate inter-individual relationships based on the results of many vertebrate studies. Recently, oxytocin has received a great deal of attention as a promising candidate for the treatment of ASD. Here, we review studies on the role of oxytocin in ASD. Numerous randomized controlled trials (RCTs) have shown single-dose oxytocin administration to have significantly favorable effects compared with placebo for both neuro-typical individuals and individuals with ASD. Furthermore, extended administration of oxytocin was associated with effects that significantly exceeded those of a placebo in three of five published RCTs for ASD. Moreover, approximately 20 RCTs investigating whether oxytocin is favorable for ASD participants are in progress, according to clinical trial registries certified by the World Health Organization. The results of these RCTs may elucidate the issues regarding favorable and adverse effects, appropriate doses and treatment durations, participant selection, and specifically how to assess the changes in impairments of social communication and social interactions. In addition, it is necessary to consider which version of the Diagnostic and Statistical Manual of Mental Disorders (DSM) is used for the diagnosis of ASD in each RCT because the range of individuals diagnosed with ASD has become gradually narrower with each DSM revision, i. e., the Fourth Edition, the Fourth Edition Text Revision, and the Fifth Edition.
 <Author's abstract>