This is a phase I study in healthy male volunteers, who will be given dexamethasone to suppress their natural cortisol production. 18 will be consented for the study. They will have had a history and a physical examination, blood tests for routine safety, hepatitis C and HIV, drug abuse and ECGs. Following the results of these tests and the inclusion/exclusion criteria for the study, they will be admitted to the phase I unit on the first afternoon (Day -1). They will be given dexamethasone at 22.00hrs that evening, and remain in the unit until the end of the period. Further dexamethasone doses will be given at 06:00, 12:00, and 18:00 hours on Day 1 (plus at 22:00 hours in patients given the modified release study drug). Each volunteer will be admitted for 3 periods of approximately 1.5 days, with a washout of 7 days between periods, and they will be randomised to either fast and take a single 20mg dose of immediate release hydrocortisone, to fast and take a single 20mg dose of the study medication, (a modified release hydrocortisone), or to the "fed" group, where they take a single dose of 20mg study medication, and have a highly calorific standardised breakfast. The volunteers will have cannulae to enable one pre-dose blood sample to be taken followed by 24 hour PK sampling (modified release) and 12 hour PK sampling for the immediate release period. After these samples have been taken the volunteers will be able to leave the unit. There will be another assessment 3 to 5 days after study period 3 with further blood tests, assessment of any adverse events etc.