My 85yr relative has been on prednisone for 40+ years. they developed short-term memory loss. prolonged prednisone use can cause a build up of cortisol in the pituitary and cause memory loss. if weaned off prednisone could they regain their memory?

You information is not all correct. Corisol does not build up in the pituitary or cause memory loss. If they really need it then stopping it all of a sudden may result in an Addisonian Crisis and death depending on how much she is taking. I am not sure who "they" is. Maybe the relative I guess but not clear. Discuss with her Dr. if she gives you permission to do so.

Agree with Dr Grim, as your pituitary information is bogus. You do not mention reasons for years of steroids. At age 85 yrs, the most likely reason for development of memory loss would be Alzheimer's disease. As mentioned, stopping prednisone will almost certainly result in adrenal crisis. A neurologist should consult and decide upon treatment.