Adrenal insufficiency is an endocrine-or hormonal-disorder that occurs when the adrenal glands do not produce enough of certain hormones. The adrenal glands are located just above the kidneys. Adrenal insufficiency can be primary or secondary.
Primary adrenal insufficiency, also called Addison's disease, occurs when the adrenal glands are damaged and cannot produce enough of the hormone cortisol and often the hormone aldosterone. Addison's disease affects one to four of every 100,000 people, of all age groups and both sexes.
Secondary adrenal insufficiency occurs when the pituitary gland-a bean-sized organ in the brain-fails to produce enough adrenocorticotropic hormone (ACTH), hormone that stimulates the adrenal glands to produce cortisol. If ACTH output is too low, cortisol production drops. Eventually, the adrenal glands can shrink due to lack of ACTH stimulation. Secondary adrenal insufficiency is much more common than Addison's disease.
This answer is based on source information from the National Endocrine and Metabolic Diseases Information Service.