A GnRH-analog that briefly stimulates the pituitary gland to release follicle stimulating hormone (FSH) and luteinising hormone (LH), but then within a few days reduces these hormones to low levels (you could say that the pituitary has had a clamp put on it), stopping these hormones from competing with administered hormones -- and, particularly in women, suppressing the LH surge that otherwise can spoil the timing of egg retrieval in an assisted conception program such as IVF or GIFT. Examples include: leuprorelin(Lucrin, made by Abbott, used in Australia and Europe) or leuprolide (Lupron, made by Abbott in the US); nafarelin (Synarel, by Syntex); goserelin (Zoladex, by ICI); triptorelin (Decapeptyl, by Ipsen Biotech and used in Europe) and buserelin (Suprefact, by Hoechst, used in Europe).

A GnRH agonist made by Abbott and sold as Lupron in the US. Called leuprorelin in Australia and Europe, and sold there as Lucrin. Administered by daily injection under the skin or as a depot preparation once per month.