Puberty blockers followed by opposite sex hormones cannot create ‘opposite sex puberty’, only secondary sex characteristics of the opposite sex. However, normal sexual or reproductive development will not occur. Girls will not begin menstruation and so will be infertile. Boys testes will not grow and develop and will impact on fertility. The change therefore is only cosmetic. A boy’s
pen will remain immature and remain the size of a child’s into adulthood. This will cause problems sexually if the
pen is retained, both functionally and in terms of sexual arousal. It is also problematic if gender reassignment surgery is later chosen since there is too little material to use from the
pen and testicles.
When a child’s natural puberty is blocked we can expect to see effects not only on the body but on the developing brain. It is the surge of sex hormones at puberty which triggers the important changes in the adolescent brain which only reach completion in the mid-twenties. Hormonal changes at puberty are thought to influence the development of both brain structure and function.
Recent research indicates that there is a window of development for some cognitive functions, and if this window is missed, cognitive development does not resume later even if blockers are discontinued. A reduction in long-term spatial memory was found to persist after discontinuation of blockers in a
recent study on sheep, which concluded:
This result suggests that the time at which puberty normally occurs may represent a critical period of hippocampal plasticity. Perturbing normal hippocampal formation in this peripubertal period may also have long lasting effects on other brain areas and aspects of cognitive function.
Two previous studies which analysed IQ performance in girls taking puberty blockers for central precocious puberty also suggest the possibility that GnRHa treatment may have an adverse impact on cognitive functioning in children. The first study of 25 children in 2001 found a drop of 7 IQ points after two years on blockers. The second study in 2016 found a drop of 8 IQ points in 15 girls compared to a matched control group.
An analysis of these studies is here.
A study in 2017 of men with late stage prostate cancer found that treatment with GnRH analogs affects cognitive functions such as language ability, short-term memory capacity, mental flexibility, and inhibitory control.