 The study is conducted as an open-label, single-arm, two-period, crossover pilot trial. Includible patients are observed for 5 weeks on their usual treatment twice or thrice daily hydrocortisone. Assessments of QoL, in terms of EMA assessments, to be used as baseline measurement in the study, are collected for 20 days preceded by a 5 days technology adaptation phase. Thereafter participants are shifted to modified release hydrocortisone Plenadren once daily OD, on a dose as per Summary of Product Characteristics SmPC. Assessments of QoL to be used as outcome of intervention in the study are performed after 12.5 weeks after initiation of Plenadren intervention treatment, in order to take into consideration the period of re-adjustment of the body after the switch from conventional hydrocortisone to Plenadren. As done at the baseline observation, EMA measurement is preceded by a five days technology adaptation phase. At the end of the intervention treatment period, the patients will be shifted to their usual hydrocortisone treatment and will be followed at the outpatient clinic according to the directives of the clinic. Biochemical parameters; blood samples, DEXA scan, 24 hour blood pressure and salivary cortisol, will be assessed at baseline and after 16 weeks, as part of the safety evaluation of Plenadren. 