• Male and female children and adolescents from 2 to \< 18 years of age with Cushing's syndrome of endogenous origin: Who have failed surgery (or) who are awaiting surgery (or) for whom surgery is not an immediate option. For patients who are awaiting surgery, the study treatment could be less than 12 weeks.

• Patients must weigh \> 10 kg.

• The diagnosis of Cushing's syndrome must be confirmed by each of the following:

⁃ 3a) The clinical criterion of decreasing growth percentiles with increasing weight (as evidenced by the presence of a contrast in height and BMI SD scores, for example a SDS \< 0 and BMI SDS \> 0, or a strong clinical suspicion of Cushing's syndrome, such as photographic evidence of a change in facial appearance); 3b) Abnormal low-dose (0.5 mg Q6h x 48 hours, or overnight 15mcg/kg \[max 1 mg\]) dexamethasone suppression test, defined as plasma cortisol levels \> 1.8 mcg/dl, at time point 48 hours (0.5 mg Q6h x 48 hours) or 9 to 12 hours (overnight 15mcg/kg \[max 1 mg\]) after the first dose of dexamethasone; (OR) Midnight serum cortisol levels \> ULN, assessed while the patient is sleeping and after pre-cannulation (OR) two samples of late-night salivary cortisol greater than ULN for the assay. 3c)Two 24-hour urinary free cortisol values \> 1.3 x ULN;

⁃ 4\. Able to swallow study drug tablets (not crushed or split) or the content of the capsules mixed with water.

⁃ 5\. Parents or legal guardians able to provide consent/assent.