Results from two clinical trials reveal that modulating the hormone vasopressin's biological pathway safely enhanced social functioning in 223 adult men and 30 children with autism spectrum disorder (ASD). The findings indicate drugs that target vasopressin could potentially help address social and behavioral deficits across diverse subpopulations of patients with the condition. Although there are several medications approved to treat ASD, they have negative side effects and do not address core symptoms such as problems with social communication and repetitive behaviors. However, an increasing body of research in mice has showed that vasopressin - a peptide that regulates social behavior in mammals - could be a promising target for new therapies. In the first study, Federico Bolognani and colleagues conducted a randomized, placebo-controlled phase 2 clinical trial where they evaluated the efficacy of balovaptan - an oral drug candidate that inhibits the receptor for vasopressin - in 223 adult men with moderate or severe ASD. The researchers split the patients into four groups and administered one of three doses of balovaptan or placebo daily for 12 weeks. They did not observe any improvements in the trial's primary endpoint as measured by the Social Responsiveness Scale or SRS (a scale that assesses social impairment in individuals with ASD). However, Bolognani et al. observed that the two patient groups that received higher doses (totaling 116 participants) displayed improvements in a second scale measuring socialization, adaptive behavior and daily living skills compared to the cohort treated with placebo (75 patients), findings that met study's secondary endpoint. Importantly, balovaptan was also well-tolerated and did not raise safety concerns, indicating it could help treat ASD in a patient group that has seen few benefits from previous trials. Taking a different approach, Karen Parker and colleagues investigated whether administering vasopressin to children with ASD could counteract social deficits. They intranasally delivered either a large dose of vasopressin or a placebo to 30 children (25 male, five female) between the ages of six and 12 for four weeks. Based on reports from the children's parents, the authors found the 17 treated children showed enhanced social behaviors as measured by the SRS (the study's primary endpoint) compared to the 13 placebo-treated individuals. Furthermore, the treated children displayed improvements in social communication as evaluated by clinicians. They were also better able to interpret the emotional and mental states of others and recognize faces in laboratory tests. Vasopressin treatment also reduced other ASD symptoms such as anxiety and was well-tolerated by the subjects.