Adrenal fatigue—more accurately described as HPA (hypothalamic-pituitary-adrenal) axis dysfunction—is a functional disorder caused by prolonged physical, emotional, or environmental stress. Over time, the stress response system becomes dysregulated, impairing the body’s ability to maintain healthy cortisol rhythms. This often results in burnout, energy crashes, anxiety, and immune suppression. Conventional testing may miss subtle patterns, but functional medicine evaluates cortisol timing, adrenal reserve, nutrient status, and root causes like mold exposure, trauma, infection, or nutrient depletion. Treatment includes rebalancing the stress response, restoring circadian rhythm, and using adaptogens, nutrients, and nervous system regulation to rebuild resilience.