TPH1(Tryptophan hydroxylase 1) is a member of the aromatic amino acid hydroxylase family. TPH1 protein catalyzes the first and rate limiting step in the biosynthesis of serotonin, an important hormone and neurotransmitter. Mutations in TPH1 have been associated with an elevated risk for a variety of diseases and disorders, including schizophrenia, somatic anxiety, anger-related traits, bipolar disorder, suicidal behavior, addictions, and others. By controlling serotonin availability, TPH1 influences monoamine metabolism and downstream signaling through serotonergic receptors that shape cellular communication, secretion, and barrier physiology. TPH1 activity is linked to pathways governing gastrointestinal and enteroendocrine function, platelet serotonin storage, and neuroimmune crosstalk in peripheral tissues. Altered TPH1 expression or peripheral serotonin balance has been associated with disorders involving gut–brain axis signaling, inflammatory processes, and metabolic regulation, making it a useful target for mechanistic studies.