Effect of Supplemental Hydrocortisone During Stress in Prednisolone-induced Adrenal Insufficiency

Who May Qualify: - Age ≥ 50 years - Women must be postmenopausal (FSH is measured at the screening visit) - A diagnosis of PMR/GCA, or both conditions combined. - Treatment with prednisolone ≥12 weeks - Ongoing prednisolone treatment, with current daily prednisolone dose \> 0 mg and ≤5 mg. The dose must have been ≤5 mg for minimum 2 weeks at the time of the screening visit. Who Should NOT Join This Trial: - Known primary or secondary adrenal insufficiency - Known Cushing's Syndrome - Known allergy towards study medication ingredients - Severe comorbidity: Heart failure (New York Heart Association class IV); Kidney failure with an estimated glomerular filtration rate \<30 mL/min (Chronic kidney disease stage 4-5); Liver disease in the form of cirrhosis; Active cancer; Known severe immune deficiency; A history of psychiatric disease requiring treatment by a psychiatric department (for affective disorders only if within the last year before study entry) - Alcohol consumption \>21 units per week - Planned major surgery during the study period at study entry. - Use of drugs that interfere with cortisol metabolism/measurements: Systemic oestrogen treatment (discontinued \< 1 month before inclusion), Treatment with strong CYP3A4 inhibitors or inducers, Use of other glucocorticoid formulations (Inhaled corticosteroids, intraarticular or intramuscular injections, steroid creams European steroid group IV-V used in the genital area. Note: Permitted glucocorticoid formulations: Eye-drops, nasal spray, glucocorticoid creams European steroid group I-III, and European steroid group IV-V used in the non-genital area only.) - Inability to provide written willing to sign a consent form. Always talk to your doctor about whether this trial is right for you.