There are many GNRH analogs today on the market, such as Lupron,
Zoladex, Abarelix, Synarel etc., for various medical purposes
requiring chemical castration. Being a synthetic analog of the LH &
FSH stimulating substance, these drugs trigger opposite effects the
first 2-3 weeks, by causing excess gonadal function, thus actually
worsening the clinical symptoms it supposed to treat.

Why would one use a hormone antagonist that actually stimulates gonadal
secretion (even if only temporary), when castration is desirable - if
one could use a LH suppressive GNIH analog instead, with immediate
effect? How come GNIH
analogs do not appear to exist in modern medicine?

Hey gualandi-ga, how are you doing?

GnRH-analogs are man-made forms of the naturally occurring hormone
GnRH (Gonadorolin); factors other than metabolic control, such as
stress, may play an etiologic role in IDDM ovarian dysfunction, and
therefore could accomodate for the "worsening the clinical symptoms".
About 50% of the oligomenorrheic IDDM adolescents had an increased
ovarian 17-OHP response to GnRH analog stimulation in the range of
functional ovarian hyperandrogenism - in the following study:

A clinical case controlled study was done to investigate the
pituitary-ovarian function in adolescent girls with insulin-dependent
diabetes mellitus (IDDM). The GnRH analog leuprolide acetate was
administered subcutaneously to 16 adolescents with IDDM (seven
eumenorrheic and nine oligomenorrheic) and 13 controls between 0800
and 0900 h.

Blood samples were then collected at baseline and 0.5, 3, 6 and 24 h
after leuprolide to measure levels of gonadotropins, 17
alpha-hydroxyprogesterone (17-OHP), androgens and estradiol.
Oligomenorrheic IDDM girls showed, as a group, a distinct 17-OHP
response to GnRH analog stimulation, which in five out of nine girls
was in the range of functional ovarian hyperandrogenism (> or = 8.6
nmol/l).

REFERENCE
European Federation of Endocrine Societies: Ovarian 17
alpha-hydroxyprogesterone responses to GnRH analog testing in
oligomenorrheic insulin-dependent diabetic adolescents; Vol 136, Issue
6, 624-629 (article).
http://www.eje-online.org/cgi/content/abstract/136/6/624

Best wishes