Telotristat is primarily used in the treatment of carcinoid syndrome, particularly in patients who experience diarrhea that is not adequately controlled by somatostatin analog therapy alone. It works by inhibiting the enzyme tryptophan hydroxylase, which reduces the production of serotonin. Excessive serotonin is a key factor in the symptoms of carcinoid syndrome, including diarrhea. By lowering serotonin levels, telotristat helps to alleviate diarrhea and improve the quality of life for patients with this condition. It is often prescribed as an adjunct therapy alongside somatostatin analogs to provide better symptom control.