Adrenal insufficiency is a condition in which the adrenal glands do not produce adequate amounts of steroid hormones. The adrenal gland normally secretes glucocorticoids (primarily cortisol), mineralocorticoids (primarily aldosterone), and androgens. These hormones are important in regulating blood pressure, electrolytes, and metabolism as a whole. Deficiency of these hormones leads to symptoms ranging from abdominal pain, vomiting, muscle weakness and fatigue, low blood pressure, depression, mood and personality changes (in mild cases) to organ failure and shock (in severe cases). An adrenal crisis may occur if the body is subjected to stress, such as an accident, injury, surgery, or severe infection; this is a life-threatening medical condition resulting from severe deficiency of cortisol in the body. Death may quickly follow.

Adrenal insufficiency can be caused by dysfunction of the adrenal gland itself, whether by destruction (e.g. Addison's disease), failure of development (e.g. adrenal dysgenesis), or enzyme deficiency (e.g. congenital adrenal hyperplasia). Adrenal insufficiency can also occur when the pituitary gland or the hypothalamus do not produce adequate amounts of the hormones that assist in regulating adrenal function. This is called secondary adrenal insufficiency (when caused by lack of production of adrenocorticotropic hormone (ACTH) in the pituitary gland) or tertiary adrenal insufficiency (when caused by lack of corticotropin-releasing hormone (CRH) in the hypothalamus).