In 1997 the Nobel prize for medicine was awarded for the discovery of the GnRH molecule and its mechanisms. By altering natural GnRH synthetic GnRH analogues can be manufactured which have a higher affinity and a longer half-life. These GnRH analogues can be subdivided into GnRH antagonists and GnRH agonists. These medications can be used where suppression of gonadotrophins and sexual hormones is an important principle of the therapy, e.g. breast cancer. GnRH analogues have been established as the standard medication for suppression of LH levels for ovarian stimulation for IVF/ICSI. Various protocols are available for ART with GnRH analogues.