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

Inclusion Criteria: * 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. Exclusion Criteria: * 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 informed consent.