Buserelin, sold under the brand name Suprefact among others, is a medication which is used primarily in the treatment of prostate cancer and endometriosis.

[3][1][2] It is also used for other indications such as the treatment of premenopausal breast cancer, uterine fibroids, and early puberty, in assisted reproduction for female infertility, and as a part of transgender hormone therapy.

[1][2][23][24] Contraindications of buserelin include the following:[1][2] During the initial phase of the therapy, before GnRH receptors have been significantly downregulated, testosterone levels are increased.

[3][1] This can lead to transient tumor activation with bone pain (in patients with cancer metastases) and urinary retention.

[3][1] Side effects that occur later during the treatment are mainly due to low sex hormone levels and include reduced libido, erectile dysfunction, hot flashes, vaginal dryness, vaginal atrophy, menorrhagia, osteoporosis, depression, asthenia, emotional lability, headache, dizziness, and application site reactions.

[3][1] By activating the GnRH receptor in the pituitary gland, buserelin induces the secretion of LH and FSH from the gonadotrophs of the anterior pituitary, which travel to the gonads through the bloodstream and activate gonadal sex hormone production as well as stimulate spermatogenesis in men and induce ovulation in women.

[3][1] The profound desensitization of the GnRH receptor results in a loss of LH and FSH secretion from the anterior pituitary and a consequent shutdown of gonadal sex hormone production, markedly diminished or abolished spermatogenesis in men, and anovulation in women.

[9][22] Sex hormone levels, including those of estradiol and progesterone, are similarly profoundly suppressed in premenopausal women.

[8][14] Buserelin is marketed in the United Kingdom, Ireland, other European countries, Canada, New Zealand, and South Africa, as well as in Latin America, Asia, and elsewhere in the world.

[8][14][34] The steroidal antiandrogen cyproterone acetate has been studied for blocking the testosterone flare at the start of buserelin therapy in men with prostate cancer.

[35][36] While cyproterone acetate for two weeks eliminates the biological and biochemical signs of the flare, no benefits on prostate cancer outcomes were observed.

[35] Very low doses of buserelin nasal spray have been assessed for increasing testosterone levels and fertility in men with oligoasthenozoospermia and hypogonadotropic hypogonadism.