Addison's disease, or adrenal insufficiency, is a chronic condition in which the adrenal glands produce insufficient levels of hormones, such as cortisol and aldosterone. When this condition becomes chronic, a similar condition known as secondary adrenal insufficiency can also result. This is caused by an impairment of the hypothalamic-pituitary-adrenal (HPA) axis, which is responsible for controlling the production and release of hormones by the adrenal glands. Secondary adrenal insufficiency is often caused by a malfunction of the pituitary gland, which can be the result of certain medications or medical conditions, such as pituitary tumors. Both Addison's disease and secondary adrenal insufficiency can cause a range of similar symptoms, including fatigue, low blood pressure, weight loss, and muscle weakness.