My 10 1/2 SW CAH boy started on Letrozole a couple months ago-  he does not have adavanced bone age.  I know that girls can not take the Letrozole because it binds estrogen so girls can not take it-  women take it after they have had breast cancer.  My son has not started puberty but the literautre says that the upside of Letorozloe over Growth Hormone is that you do not delay puberty.  So  I would think if you wanted to delay puberty that Letrozole would not be the right choice --it prevents growth plates from closing so the boys can continue to grow.  I have not seen any side effects so far.

 

Good luck.