"I have read that it can take up to 6-12 months for the adrenal glands to fully recover after the long term use of prednisone."
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That was consistent with my experience after long term prednisone use. However, my endocrinologist said I had to stay on a low dose and wait for my adrenals to recover. She defined a low dose was approximately 3 mg because it wasn't safe for me to taper any lower.

I was on 3 mg for 6 months and felt miserable. Fortunately I didn't have a PMR flare. I guess my adrenals were making just enough cortisol to regulate my baseline inflammation. A steroid sparing medication which didn't suppress my adrenal function was keeping the excess PMR inflammation in check.

Sometimes the textbook says it can take 1 month for the adrenals to recover for every month we are on prednisone. I don't think this is true. I was on prednisone for 12 years and it didn't take 12 years for my adrenals to recover. However, I'm still not sure my adrenals have "fully recovered."

Cortisol levels fluctuate based on circumstances related to the amount of stress we are under. The more stress we have, the more cortisol we need. When we replace cortisol with prednisone the same thing applies. The more stress we have the more prednisone we need.

When I stopped prednisone my endocrinolgist said, "I should take prednisone again for any reason if I felt the need." She had no way of predicting the amount of stress I would experience going forward after I stopped Prednisone.