When administered at high doses mifepristone exhibits antiglucocorticoid activity and therefore maybe be useful alternative to currently used medical treatments. Antiglucocorticoid antagonists prevent the biological effects of glucocorticoids by competing with theses hormones for binding to the intra-cellular glucocorticoid receptor. Mifepristone is the first potent glucocorticoid antagonist active in vivo. Mifepristone can act as both an optimal antagonist (devoid of any agonist activity) or a suboptimal antagonist (partial agonist antagonist), depending on the response examined.

The antiglucocorticoid effect of Mifepristone has been studied in patients with Cushing's syndrome. Case reports indicate that treatment with mifepristone 400 to 800mg daily or 20mg/Kg daily may be effective in resolving the biochemical abnormalities associated with Cushing's syndrome i.e. hupokalaemic alkosis, hyperglycaemia, abnormal TSH, LH and testosterone. It may also be effective in reducing/eliminating the clinical abnormalities associated with Cushing's syndrome as noted above.

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