Telotristat ethyl is primarily used in the treatment of carcinoid syndrome, a condition often associated with neuroendocrine tumors. It works by inhibiting the enzyme tryptophan hydroxylase, which is involved in the production of serotonin. By reducing serotonin levels, it helps alleviate symptoms such as diarrhea that are commonly experienced by patients with carcinoid syndrome. This medication is particularly beneficial for patients who have not responded adequately to somatostatin analog therapy, offering an additional option for managing their symptoms and improving their quality of life.