Autism
In 1982, three autistic children with hyperserotoninemia were reported to have had an impressive clinical response to treatment with fenfluraminea finding that generated considerable hope and excitement. Now, well-designed studies have evaluated both the relationship of serotonin levels to autism and the clinical and biochemical effects of fenfluramine.
Blood serotonin levels are not universally elevated in children with autism, and mean blood serotonin concentrations in autistic children are not significantly different from those in normal or in nonautistic retarded children. Treatment with fenfluramine does cause significant decreases in blood serotonin concentrations in autistic children, but such biochemical changes are not associated with changes in psychometric measurements of general intelligence.