Addison's disease is also known as hypoadrenocorticism. It is an insufficient production of adrenal hormones by the adrenal gland. Since these hormones are essential for life, this is an extremely serious disease and it must be treated as such.
Adrenal insufficiency can be primary or secondary.
Secondary adrenocorticism usually only affects the glucocorticoids. Secondary adrenocorticism probably occurs most often when prednisone or other cortisone being administered for medical reasons are suddenly withdrawn. It can occur as a result of pituitary cancer or some other process that interferes with production of hormones that stimulate the adrenal glands. Most dogs with Addison's disease initially have gastrointestinal disturbances like vomiting. Lethargy it also a common early sign.