I was on the small doses of hydrocortisone treatment for about 4 months and did feel better pus my thyroid replacement seemed to work better. But then DH got laid off, lost health insurance, etc. Luckily I had enough left to slowly wean off the hydrocortisone. Surprisingly, I think the 4-month treatment might have been just about right for me. I've had no ill effects after stopping.

An excellent book on the subject is William McK. Jeffries "Safe Uses of Cortisol."