@mezack25

Prednisone is a synthetic form of the naturally occurring hormone called cortisol. In essence, prednisone replaces the cortisol that our adrenals produce. After "long term" prednisone, it takes a long time for our adrenals to start producing cortisol again.

Medical sources say cortisol levels decrease after one dose of prednisone. The ability of the adrenals to produce cortisol is suppressed as soon as 3 weeks after starting Prednisone The following is what Mayo says:

"Prednisone is like cortisol, a hormone naturally made by your adrenal glands. If you take prednisone for more than a few weeks, your adrenal glands decrease cortisol production. A gradual reduction in prednisone dosage gives your adrenal glands time to resume their usual function."
https://www.mayoclinic.org/diseases-conditions/inflammatory-bowel-disease/expert-answers/prednisone-withdrawal/faq-20057923.
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The longer we take Prednisone, more time is needed for the adrenals to start producing cortisol again. This is probably the most important reason why Prednisone can't be abruptly stopped and why we must taper slowly.

"When you taper off prednisone, your adrenal glands have time to catch up and make normal levels of cortisol. This could take weeks or even months, depending on how long you took the medication or how high your dose was."
https://www.webmd.com/rheumatoid-arthritis/prednisone-taper
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I took Prednisone at moderately high doses for 12 years. When Actemra allowed me to taper off Prednisone, I needed a year for my adrenals to recover. I had to stay on 3 mg of Prednisone for 6 months because of a low cortisol level. When I had adrenal insufficiency, 3 mg of Prednisone was my "maintenance dose" to compensate for a low cortisol level. After 12 years on Prednisone, my endocrinologist wasn't very optimistic about me ever being able to discontinue Prednisone completely.

After 6 months on 3 mg of Prednisone, my endocrinologist said my cortisol level was "adequate" but she didn't know what would happen if Prednisone was stopped. When I decided to stop prednisone, I was told to restart prednisone again for "any reason if I felt the need." When I stopped prednisone, I had a need to restart it again a couple of times for multiple reasons. However, I never had a PMR flare as long as I took Actemra.

My symptoms adrenal insufficiency (overwhelming fatigue) persisted for more than a year after I first stopped Prednisone.

My endocrinologist said any amount of Prednisone will suppress the ability of my adrenals to produce cortisol again. She "encouraged" me to stay off Prednisone if I could. Since Actemra controls PMR, I don't need Prednisone for PMR anymore. Actemra doesn't suppress my adrenal function. I haven't needed Prednisone for about 5 years.