Physician's Best A naturally occurring tryptophan metabolite is present in 5-HTP (5-hydroxy L-tryptophan). 5-HTP is taken out of Griffonia simplicifolia plant seeds. Serotonin is a neurotransmitter that is produced in the brain from 5-HTP and is present in the synapses, or connections, between neurons. It has a soothing and relaxing impact, supporting the maintenance of mental and emotional well-being as well as encouraging restful sleep.