BackgroundThis study examined the 52-week safety and efficacy of AST-001 syrup for the core symptoms of autism spectrum disorder (ASD) in children aged 2–11 years.MethodsThis multicenter long-term follow-up study enrolled children with ASD who were identified as responders in an antecedent phase II randomized controlled trial. A total of 61 participants were given the same dose (high or low) they received during the extension phase of the phase-II trial for 52 weeks. Safety and tolerability were