Which drug also acts as a GnRH agonist used in treating endometriosis?

Goserelin is a synthetic analog of gonadotropin-releasing hormone (GnRH) that acts as a GnRH agonist. It is used in treating conditions such as endometriosis by regulating sex hormone levels in the body. By stimulating the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH) initially, goserelin can lead to a subsequent downregulation of the receptor, leading to decreased levels of estrogen and progesterone, which are critical in sustaining the growth of endometrial tissue. This makes it particularly effective in managing the symptoms associated with endometriosis.

The other options revolve around different mechanisms or therapeutic indications. For instance, ribociclib is primarily used as a cancer treatment, particularly for breast cancer, and does not have a role as a GnRH agonist. Nilutamide and casodex, while both are anti-androgens used primarily in prostate cancer treatment, do not function as GnRH agonists and therefore would not be relevant in the context of treating endometriosis.