Suppresses it. Taking the hormone that is normally produced by the adrenal cortex means that it no longer produces it (negative feedback). If you suddenly stop taking the medication, your body needs several days to weeks to begin to make hormone again. So, if you are taking cortisol you need to taper the dose to make sure you give your glands the chance to being producing again.
Prolonged use, yes. Using steroid for a brief period of time of less than a few weeks probably won't have long term effect, but prolonged use will suppress it--it loses the ability to produce the steroid. Thus folks who need to use steroid for an extended of time often need to remain on it. The length of time varies, but using more than 3 wks typically would need a slow wean. Consult doc. Good luck.
Supression. Adrenal gland produces cortisol. External sources of cortisol (cortisone) will suppress the normal adrenal function.