Targeting the Neurobiology of RRB in Autism Using N-acetylcysteine: Single-dose

Inclusion Criteria: * children between 3 years and 12 years 11 months at the time of consent * diagnosis of Autism Spectrum Disorder confirmed with the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule-2 (ADOS-2), or Brief Observation of Symptoms of Autism (BOSA), or Childhood Autism Rating Scale- Second Edition (CARS-2). * at least moderate Restricted and Repetitive Behaviors severity defined by a Children's Yale-Brown Obsessive Compulsive Scale for children with autism spectrum disorder score ≥ 11, * physical development indicative of prepubescence as defined by the criteria for Tanner Stage 1, * medically stable, * passes MR safety screening (e.g., no metal in the body). Exclusion Criteria: * presence of known genetic abnormalities associated with Autism Spectrum Disorder (e.g. Fragile X), * current or life-time diagnosis of severe psychiatric disorder (e.g., schizophrenia), * presence of significant medical problems that would interfere with participation, * the inability of at least one caregiver to speak/read English to a sufficient level to complete study requirements and materials, * individuals taking antioxidant agents and glutathione prodrugs, or * the inability/unwillingness to swallow an agent during the screening visit.