GnRH receptor antagonists are disclosed that have utility in the treatment of a variety of sex-hormone related conditions in both men and women. The compounds of this invention have the structure: ##STR00001## wherein R.sub.1a, R.sub.1b, R.sub.1c, R.sub.2a, R.sub.2b, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and X are as defined herein, including stereoisomers, prodrugs and pharmaceutically acceptable salts thereof. Also disclosed are compositions containing a compound of this invention in combination with a pharmaceutically acceptable carrier, as well as methods relating to the use thereof for antagonizing gonadotropin-releasing hormone in a subject in need thereof.