Osteoporosis is a major adverse effect caused by the glucocorticoids. It is due to their ability to(Lippincott's 3rd pharmacology)

B. i.e. (Inhibit absorption of calcium) (314- Lippincott's 3rd)Glucocorticoid- induced osteoporosis is attributed to inhibition of calcium absorption as well as bone formation.Increased intake of calcium plus vitamin D or calcitonin or of other drugs that are effective in this condition is indicated.Glucocorticoids suppress rather than stimulate the hypothalamic -pituitary- adrenal axis. The decreased production of prostaglandins does not play a role in bone formation.