One message that has become louder over the past few years is the need for diagnosing a child's autism as early as possible so intense therapy can begin as early as possible. The thinking is that when a child is 2 or 3 and the brain is still developing, intense behavioral therapy might reduce the disruptive behaviors and teach the child skills that will lead to greater independence as he or she gets older. The researchers who reviewed studies published between 2000 and 2010 found that two types different types of intensive behavior therapy (the Lovaas or classic Applied Behavior Analysis or ABA and the Early Start Denver Model) seemed to help children improve cognitive development, language skills. But ,the evidence that shows who benefits most is insufficient or lacking.
Medical and Behavioral Therapies for Autism - Recent Studies and Confirmation of Efficacy of Applied Behavior Analysis Early Intervention
This article mentions that serotonin has been studied sufficiently to confirm that it is not therapeutic for autism and that "risperidone and aripiprazole, which are FDA-approved to treat patients with autism, were shown to be beneficial" ; however do not address core characteristics, obviously, and side effects are to be considered seriously. references to the actual studies are included.