There are various reasons why the body may produce too much cortisol, and complex tests may be needed to find the root cause of the excess cortisol. The most common cause of excess cortisol is a small, non-cancerous tumour in the pituitary gland which makes too much of a hormone called ACTH which stimulates the adrenal glands to make too much cortisol. This tumour can usually be removed by surgery.
This is a companion discussion topic for the original article at https://patient.info/hormones/cushings-syndrome-leaflet