Pilot Study to Characterize and Examine the Pharmacokinetics and Efficacy of Chronocort® in Adults With CAH

Inclusion Criteria: 1. Known CAH due to 21-hydroxylase deficiency (classic CAH) based on hormonal and genetic testing currently treated with hydrocortisone, prednisone, prednisolone or dexamethasone on a stable dosage for a minimum of 3 months. 2. Male or female patients aged 18 and above. 3. Provision of signed written informed consent. 4. Good general health. 5. Females of childbearing potential must have a negative pregnancy test initially and at all visits. Females who are engaging in sexual intercourse must be using a medically acceptable method of contraception (as defined in the protocol, section 10.5). 6. Plasma renin activity must be within the clinically acceptable range at screening (less than 1.5 times upper normal range). Exclusion Criteria: 1. Co-morbid condition requiring daily administration of a medication that induces hepatic enzymes or interferes with the metabolism of glucocorticoids. 2. Clinical or biochemical evidence of hepatic or renal disease. Creatinine above the normal range or elevated liver function tests (ALT or AST) \> 2 times the upper limits of normal. 3. Females who are pregnant or lactating. 4. Women taking an estrogen-containing oral contraceptive pill and who have taken it within 6 weeks of recruitment. 5. Patients taking spironolactone. 6. Patients on inhaled or oral steroids apart from treatment for CAH. 7. Patients with any other significant medical or psychiatric conditions that in the opinion of the Investigator would preclude participation in the trial. 8. Participation in another clinical trial of an investigational or licensed drug or device within the 3 months prior to inclusion in this study. 9. Patients with history of bilateral adrenalectomy.