Adrenal fatigue is a term that's used by some to say that fatigue and other symptoms are caused by a poorly working adrenal gland in people who are under mental, emotional, or physical stress. But it's not a proven medical condition. Your adrenal glands make hormones. One of these is cortisol, which helps your body deal with stress. According to the adrenal fatigue theory, if your life is too stressful, your adrenal glands may not pump out enough hormones, leading to a wide variety of symptoms. But there's no evidence to support this theory.