The present invention describes methods of treating a pituitary tumor, methods of suppressing ACTH and/or corticosterone levels in an ACTH-secreting pituitary adenoma, methods of inhibiting the growth of an ACTH-secreting pituitary adenoma and methods of treating Cushings disease. These methods can include providing a composition comprising R-roscovitin or a salt thereof and administering the composition to a mammalian subject in need thereof.