Gonadotrophin-releasing hormone agonist (GnRHa) is commonly used to switch off (down regulate) the pituitary gland and thus suppress ovarian activity in women undergoing in vitro fertilisation (IVF). Other fertility drugs (gonadotrophins) are then used to stimulate ovulation in a controlled manner. Among the various types of pituitary down regulation protocols in use, the long protocol achieves the best clinical pregnancy rate. The long protocol requires GnRHa administration until suppression of ovarian activity occurs, within approximately 14 days. GnRHa can be used either as daily low-dose injections or through a single injection containing higher doses of the drug (depot). It is unclear which of these two forms of administration is best, and whether single depot administration may require higher doses of gonadotrophins.