Leuprorelin is a pharmaceutical hormone preparation that acts like GnRH. It is usually used to treat prostate cancer, but is also used to treat breast cancer, endometriosis, uterine fibroids and precocious puberty. It works by reducing gonadotropin, a precursor to testosterone. Common side effects are hot flashes, mood swings, insomnia, headache and pain at the injection site. It may also cause high blood sugar, an allergic reaction and problems with the pituitary gland. It is contraindicated during pregnancy.