PRL and Tinnitus: However, in a study of patients with chronic subjective tinnitus, hormone levels, including ACTH, β-endorphin, prolactin, and urinary catecholamine did not change according to the stress score, but ACTH was associated with immunosuppression markers related to stress response [56] In addition, serotonin (5-hydroxytryptamine, 5-HT), synthesized and secreted by the brain in stressful situations, plays an important role in filtering and regulating auditory information, and abnormal serotonin secretion and synthesis are considered to be one of the processes of recognizing tinnitus [57].