Abstract Disclosure: M. Dillon: None. S. Shteyman: None. W. Rashid: None. B.P. Ramchandani: None. A.G. Samat: None. Introduction: Hormone-sensitive cancers, including prostate and breast cancer, and some gynecological conditions can be treated with GnRH agonists, including leuprolide. However, pituitary apoplexy is a rare potential complication after administration. Case Description: 71-year-old gentleman with metastatic hormone-sensitive prostate cancer presented with an acute headache after receiving a dose of leuprolide. This was his first GnRH agonist dose after prior Degarelix treatment. After two hours, the patient developed a constant throbbing headache, palpitations, left eye tearing and non-bilious non-bloody vomiting. Vitals were within normal ranges, and initial lab work showed low serum cortisol of 4.6. CT scan of the head showed exophthalmos and a mildly enlarged sella. Subsequent MRI demonstrated pituitary hemorrhage and optic chiasm impingement from resulting swelling. Hormone levels remained normal. Since the patient did not develop visual field defects or other ocular complaints, the decision was to manage the patient medically rather than with surgery. The day after admission, he developed hypotension requiring high dose steroids. After discharge, outpatient repeat MRI showed interval resolution of hemorrhage into a predominantly cystic pituitary macroadenoma. Discussion: With continued stimulation, GnRH agonists desensitize the pituitary and cause a downregulation of hormonal induced cancer growth. However, there is an initial transient burst of stimulation that can induce pituitary apoplexy in patients who already have a large adenoma. The hemorrhage and subsequent swelling cause a sudden severe headache and possible visual loss or hypopituitarism. This is life-threatening due to hypotension from catecholamine insensitive blood vessels in the absence of cortisol. Treatment involves high dose steroids, frequent sodium checks and possible emergency neurosurgery for decompression. It is important with GnRH agonists to watch out for this rare complication, whether the hormonal axis is being suppressed for metastatic cancer treatment or for hormonally driven gynecological conditions. Sources: Briet C, Salenave S, Bonneville JF, Laws ER, Chanson P. Pituitary Apoplexy. Endocr Rev. 2015 Dec;36(6):622-45. doi: 10.1210/er.2015-1042. Epub 2015 Sep 28. PMID: 26414232. Tanios G, Mungo NA, Kapila A, Bajaj K. Pituitary apoplexy: a rare complication of leuprolide therapy in prostate cancer treatment. BMJ Case Rep. 2017 Jul 14; 2017:bcr2016218514. doi: 10.1136/bcr-2016-218514. PMID: 28710301; PMCID: PMC5534692. Presentation: Saturday, June 17, 2023