5-HTP & Autism

Autism is a term used to describe a diverse group of disorders characterized by impaired communication, limited social interaction and repetitive or restricted patterns of behavior. According to Dr. Jeremy Parr at the University of Oxford in the United Kingdom, most cases of autism are caused by genetic factors. Scientists have learned that metabolism of the neurotransmitter serotonin and its precursor, 5-HTP, is disturbed in many autistic patients, but the nature of this disturbance is not well understood. 5-HTP should not be used to treat autism without consulting a physician.

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Serotonin Pools

Serotonin is involved in an array of physiologic and neurologic processes, including mood, appetite, sexual behavior, sleep, motivation, digestion and blood clotting. Your body possesses two serotonin pools – one in your brain and one in your peripheral tissues. In both pools, serotonin is produced from the enzymatic conversion of the amino acid L-tryptophan to 5-HTP and then to serotonin. Serotonin from your peripheral pool does not cross efficiently into your brain pool, but 5-HTP readily crosses the "blood-brain barrier."

Serotonin Turnover

When an electrical impulse travels down a nerve, serotonin is released into the microscopic spaces called synapses between adjacent nerves, transmitting the impulse from one nerve to the next. As the impulse passes, serotonin is reabsorbed into the “upstream” nerve, where it is stored until the next impulse arrives. Your brain’s ability to maintain serotonin turnover is critical for your day-to-day function. In 2007, by measuring responses to 5-HTP administration, Belgian scientists demonstrated deficiencies in serotonin turnover in the brains of 18 autistic patients. It is believed that serotonin deficiencies could play a role in the symptoms of many autistic individuals.

Genetic Associations

Scientists have only begun to shed light on the connections between genetics and autism. In the March 2011 issue of “Molecular Genetics and Metabolism,” Swiss researchers described specific genetic abnormalities that caused accelerated reabsorption of serotonin in the central nervous system of one autistic child, leading to decreased serotonin levels in the patient’s brain synapses. This child’s autistic behavior was partially improved by treatment with 5-HTP, which was presumed to increase brain serotonin levels. It is not yet clear if similar results would be seen in other autistic individuals.


Autism is a complex disorder whose causes are not clearly defined. Genetic influences play a large role, and genetic markers associated with disrupted serotonin turnover have been identified in some patients. Because it readily crosses from your bloodstream to your brain, 5-HTP has been used to study serotonin abnormalities in the brains of autistic individuals, and 5-HTP treatment has even improved autistic symptoms in selected patients. However, it is not clear if 5-HTP has a place in treating autism, and it should not be used for this purpose without medical supervision.