Cushing's syndrome (CS) is a disorder associated with significant morbidity and mortality due to prolonged exposure to high cortisol concentrations.

Our objective was to evaluate the safety and efficacy of mifepristone, a glucocorticoid receptor antagonist, in endogenous CS.

We conducted a 24-wk multicenter, open-label trial after failed multimodality therapy at 14 U.S. academic medical centers and three private research centers.

Participants included 50 adults with endogenous CS associated with type 2 diabetes mellitus/impaired glucose tolerance (C-DM) or a diagnosis of hypertension alone (C-HT).

Mifepristone was administered at doses of 300-1200 mg daily.

We evaluated change in area under the curve for glucose on 2-h oral glucose test for C-DM and change in diastolic blood pressure from baseline to wk 24 for C-HT.

In the C-DM cohort, an area under the curve for glucose (AUC_glucose) response was seen in 60% of patients (P < 0.0001). Mean ± sd glycated hemoglobin (HbA1c) decreased from 7.43 ± 1.52% to 6.29 ± 0.99% (P < 0.001); fasting plasma glucose decreased from 149.0 ± 75.7 mg/dl (8.3 ± 4.1 mmol/liter) to 104.7 ± 37.5 mg/dl (5.8 ± 2.1 mmol/liter, P < 0.03). In C-HT cohort, a diastolic blood pressure response was seen in 38% of patients (P < 0.05). Mean weight change was −5.7 ± 7.4% (P < 0.001) with waist circumference decrease of −6.78 ± 5.8 cm (P < 0.001) in women and −8.44 ± 5.9 cm (P < 0.001) in men. Overall, 87% (P < 0.0001) had significant improvement in clinical status. Insulin resistance, depression, cognition, and quality of life also improved. Common adverse events were fatigue, nausea, headache, low potassium, arthralgia, vomiting, edema, and endometrial thickening in women.

Mifepristone produced significant clinical and metabolic improvement in patients with CS with an acceptable risk-benefit profile during 6 months of treatment.