Adrenal fatigue is a reaction to increased cortisol being released by the adrenal glands. Cortisol is a hormone used in the regulation of blood pressure. Adrenals release greater amounts of cortisol, usually in response to stress.
Adrenal fatigue is thought be a result of overtaxed adrenals caused by an excessive cortisol response. As a result, the Adrenals can no longer produce levels of cortisol necessary for optimal body function.