Inhibitors of steroid synthesis such as o,p'-DDD, aminoglutethimide, metyrapone, trilostane and ketoconazole are usually used for treatment of Cushing's syndrome in order to reduce the steroid production in the patients showing several complications, including severe hypertension and diabetes mellitus, and also an incomplete remission after the surgical treatment. o,p'-DDD and metyrapone are recommended to use for treatment of adrenocortical cancer and rapid reduction of cortisol levels, respectively. Aminoglutethimide and trilostane do not always have any side effects, although ketoconazole which is commonly used for treatment of Cushing's disease shows severe hepatic damage. RU 486 is effective for inhibiting the activity of glucocorticoid receptor, and will be used for treatment of Cushing's syndrome in near future.