Hypothalmic-pituitary-adrenal (HPA) axis suppression

This is the most common cause of adrenal insufficiency 

Long-term use of gluccocorticoids can cause this, and it is characterized by:

low CRH

low ACTH

low cortisol

The patient will have a low BP due to the low cortisol

In a healthy individual CRH stimulates ACTH which in turn stimulates Cortisol.

Normally Cortisol provides negative feedback for CRH and ACTH so when a patient has ectopic secretion of cortisol you will see decreased CRH and ACTH