GnRH Agonists and PCOS

Some patients with ovulation disorders have very little hormone coming from the pituitary gland to the ovary. FSH treatment therefore works very well in this group. However patients with PCOS have very mixed and disorganised messages of FSH and LH coming from the pituitary gland to the ovary. When external FSH is administered by injection and eggs begin to grow in the PCOS ovary the pituitary gland still has the ability to interfere with orderly egg development, maturation and release.

It is therefore sometimes helpful to block the effect of the pituitary gland using a special class of hormones called GnRH agonists. These hormones have a structure very similar to GnRH but are up to 1,000-2,000 times more powerful. When administered they go to the pituitary gland and rapidly exhaust all remaining stocks of FSH and LH hormone. The pituitary gland temporarily therefore stops releasing these hormones. The ovary is then able to be stimulated using FSH injections without any interference from the now blocked pituitary gland.

GnRH Agonists Available in Australia include:

Lucrin (Leuprorelin Acetate)

This is administered each day by a small subcutaneous injection.

Synarel (Naferalin)

This is given as a nasal spray. The spray is administered twice a day, once in the morning and once in the evening. Each bottle of nasal spray lasts 28 days.


This is a depot-injection. A small pellet of GnRH agonist is injected under the skin. The pellet dissolves over 28 days. Zoladex is useful for treating endometriosis but is less helpful in infertility patients as GnRH agonists are better not used in early pregnancy. A depot-injection like Zoladex would often continue to have its effect in early pregnancy whereas Lucrin and Synarel can be ceased soon after ovulation occurs.

GnRH agonists can cause headache, nausea, hot flushes, and mood disturbance. However many of these side effects occur when the GnRH agonist is used for a significant length of time e.g. several months for treating endometriosis. When used over a short time period with FSH the side effects are minimal as the effects of the GnRH agonist are rapidly reversed by oestrogen build up associated with egg development.