Repetitive thoughts and behavior are considered integral and core components of autistic disorder. Results from recent studies suggest that the types of repetitive thoughts and behavior of adults with autism and those with obsessive-compulsive disorder (OCD) may be different. Serotonin reuptake inhibitors (SRIs), the primary drug treatment for patients with OCD, may reduce the repetitive phenomena of some autistic patients. Two controlled studies of the nonselective SRI clomipramine have shown the drug to be more efficacious than the relatively selective norepinephrine reuptake inhibitor desipramine and placebo in children with autism. One controlled study of the selective SRI fluvoxamine found it to be significantly better than placebo for reducing repetitive phenomena and aggression in adults with autistic disorder. Additional research is needed.