Four Weeks of Intranasal Oxytocin in Autism: No Social Improvement but Lasting Reductions in Repetitive Behaviors Up to One Year

This was a double-blind, randomized, placebo-controlled, parallel-group pilot trial (Eudract 2014-000586-45). Forty adult men with ASD received either intranasal oxytocin (24 IU once daily in the morning) or placebo for 4 weeks. Assessments were conducted at baseline, immediately post-treatment (~24 hours after last dose), 4 weeks post-treatment, and 1 year post-treatment. Outcomes included self-report and informant-based questionnaires measuring social responsiveness, repetitive behaviors, attachment style, and mood states.

This is one of the first oxytocin trials in autism to include long-term follow-up (up to 1 year). While the failure to improve core social symptoms is disappointing, the discovery of lasting effects on repetitive behaviors and avoidance is intriguing because: (1) repetitive behaviors are a core autism feature that significantly impacts quality of life, (2) effects persisting 1 year after only 4 weeks of treatment suggest oxytocin may trigger lasting neural changes rather than just temporary chemical effects, and (3) this shifts the conversation about which autism features oxytocin might actually help.

Oxytocin has been one of the most studied neuropeptides for autism intervention, with mixed results across trials. This study contributes the important finding that oxytocin's benefits may not lie where researchers initially expected (social cognition) but in adjacent domains (repetitive behaviors, attachment avoidance). The long-lasting effects are particularly significant — most peptide drugs have effects that wear off quickly, but oxytocin may promote neural plasticity that persists long after treatment. This could shift the oxytocin-autism research field toward new outcome measures and treatment paradigms.

This is a small pilot study (n=40) with multiple secondary outcome comparisons, increasing the risk of false positive findings. The p-values for significant secondary outcomes (0.03-0.04) would not survive correction for multiple comparisons. Only adult men were included, limiting generalizability to women and children with autism. Self-report measures are inherently subjective, particularly for individuals with ASD who may have difficulty with self-assessment. The strong placebo response in social responsiveness measures is notable and complicates interpretation. The 24 IU dose and once-daily regimen may not be optimal.