Used to treat carcinoid syndrome diarrhea in patients who are not adequately controlled by somatostatin analogs alone. It works by inhibiting tryptophan hydroxylase, the enzyme responsible for serotonin production in neuroendocrine tumors. By reducing excessive serotonin synthesis, it helps decrease bowel movement frequency and improves overall symptom control. Often used as an add-on therapy in long-term management of carcinoid syndrome.