used in treatment of endometriosis since early 1980s
induce a reversible pseudomenopause
bind to pituitary GnRH receptors and result in a stimulation of follicle-stimulating hormone (FSH) and luteinising hormone release; GnRH analogues have much longer half-life than natural GnRH and therefore the pituitary is exposed to continuous GnRH stimulation resulting in a down regulation of the pituitary and consequent reduction of FSH and LH levels. Oestrogen levels equivalent to postmenopausal levels are achieved within about 3 weeks of initiation of therapy
oestrogen deficiency related e.g. vaginal dryness, hot flushes, reduction of libido, bone loss
duration of GnRH analogue treatment is limited by side effects, especially bone loss (1); addback therapy is used to help prevent or reduce bone loss secondary to GnRH analogue therapy. Various addback therapies have been tried including progestogens, tibolone, bisphosphonates and combined oestrogen/progestogen. The addback therapy should not negate the treatment effect of the GnRH analogue on the endometriosis
1) Johansen JS et al (1988). The effect of GnRH agonist on bone metabolism. J Clin Endocrinol Metab, 67, 701-6.