More About Serotonin.
The word comes from the combination of sero- (serum) + tonic (from Greek tonos string or stretching) + -in (from Latin -ina a term used to form words). It was first named in 1948, although its effects had likely been observed since 1868.
Serotonin is a neurotransmitter hormone synthesized in the adrenal glands and elsewhere in the body from the essential amino acid tryptophan (chemical formula C10H12N2O, also called 5-hydroxytryptamine), found in the brain, blood, and mostly the digestive tract, which allows nerve cells throughout the body to communicate and interact with each other.