NPY is decisively involved in modulating the stress response systems like the hypothalamic–pituitary–adrenal axis system and, thereby, in the regulation of stress and anxiety, trauma-induced disorders, depression, chronic fatigue syndrome, cognition, learning and memory, information handling, neuroprotection, circadian rhythm, energy homeostasis, food intake, sexual behavior, migraine, epilepsy, schizophrenia, alcoholism, and addiction (10, 11). This evidence concerns the gene NPY and major depressive disorder.