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.