DOSCORT is a 2-dose, cross-over study primarily aiming to identify and validate novel biological markers (biomarkers) of glucocorticoid effect in the human body. Patients with Addison´s disease, primary adrenal insufficiency, with life-long glucocorticoid replacement therapy will undergo 2 treatment periods where their usual hydrocortisone treatment will be replaced with dexamethasone in physiological and supra physiological doses. Blood, saliva, urine, health related Quality-of-life self-assessment forms, measurements of physical activity and sleep quality will be collected from both treatment periods.