Depression is a mood disorder influenced by hormonal regulation, where testosterone, TRT, HRT, or prior anabolic-androgenic steroid exposure affect neurotransmitter balance, neuroinflammation, energy regulation, and stress resilience, making both deficiency and excess, hormone fluctuations, and therapy stability central to symptom development, emotional well-being, and management through a Testosteronology®-informed, endocrine-centered approach.