What is Serotonin?
Serotonin is a monoamine neurotransmitter synthesised from tryptophan, predominantly in enterochromaffin cells of the gut and in serotonergic neurones of the central nervous system. Peripherally, serotonin modulates gastrointestinal motility, platelet aggregation, and vascular tone; centrally, it regulates mood, sleep, appetite, and cognition. Urinary serotonin reflects predominantly peripheral turnover rather than central compartment activity, and interpretation of urinary levels as a proxy for brain function remains exploratory.