@dadcue This is very interesting and, yes, always difficult to tease out. When (with hindsight) the methotrexate first began to poison me, my CRP went up very high and my dose of pred was doubled to 20 mgs for 3 days then brought down to 15 mgs, which I was on for 5 days before I could no longer walk from pain and weakness in the hamstrings. Ended up in hospital emergency who gave me an IV of 30 mgs hydrocortsione and within 2 hours I could walk without major issues. Discharge papers listed adrenal insufficiency as the diagnosis. GP said it was unlikely and probably a virus, and then spent the next 6 months convincing me that methotrexate had nothing to do with my declining health, which had escalated to raging fevers every week after the methotrexate dose. Stopped taking methotrexate in June after hospital doctors diagnosed toxicity and a whole range of bad symptoms ceased within several days. Two months later and my exceedingly poor blood cell count had returned to normal. So it looks like the hospital was correct in diagnosing adrenal insufficiency even around 15-20 mg of pred.