Close examination of existing studies indicates that use of puberty blockers in transgender young people commonly results in loss of bone mineral density

Writing in this journal, Cohen and Barnes clearly articulate the ongoing debate in relation to the effects of puberty blockers (Gonadotrophin Releasing Hormone agonists; GnRHa) on bone density in trans and gender diverse (TGD) young people. In particular, contention remains as to whether GnRHa causes slow accrual relative to pubertal controls, static accrual or bone loss.
Contributing to this confusion is that bone mineral density (BMD) in adolescents is typically reported as a Z-score that is adjusted for sex, height and age (height-for-age Z, HAZ) and based on normative population data (1, 2).

Significant reductions in HAZ during GnRHa treatment have been widely reported (3-7), and generally interpreted as poor accrual relative to pubertal population norms (3). However, HAZ scores decline with slow relative accrual, static accrual and actual BMD loss, and cannot distinguish between any of these different scenarios. Thus, we would argue that HAZ scores have limited utility in assessing an adolescent undergoing pubertal suppression.


https://www.bmj.com/content/366/bmj.l5647/rr-0