Cetrorelix acetate is an injectable gonadotropin-releasing hormone (GnRH) antagonist. A synthetic decapeptide, it is used to treat hormone-sensitive cancers of the prostate and breast (in pre-/perimenopausal women) and some benign gynaecological disorders (endometriosis, uterine fibroids and endometrial thinning).

Cetrorelix is marketed for use in in-vitro fertilization in all countries except Japan, where it is marketed by Shionogi and Nippon Kayaku. Aeterna Zentaris receives royalties on these sales and retains rights to develop cetrorelix for other indications.
In IVF use it is injected daily after follicle stimulation has been initiated and evidence of follicle maturation is approaching; given daily it prevents an endogenous LH surge that would trigger an untimely ovulation prior to the hCG administration by the treating physician. As an alternative to the GnRH antagonist, also a GnRH agonist could be given, but agonist have to be started earlier to overcome the agonistic effect. Cetrorelix can be mixed with follitropin alpha without compromising their reported safety and efficacy.