GnRH agonist appears to have a direct effect in endometrial cells cultures, by enhancing the percentage of apoptotic cells and decreasing the release of pro-mitogenic cytokines such as interleukin 1beta (IL-1b) and vascular endothelial growth factor during the proliferative phase to inhibit endometriosis [26], but increased IL-1b expression in the mid luteal phase of the menstrual cycle to help implantation [27]. Here, IL1B is linked to endometriosis.