> With puberty blockers and in adults treated with GAHT, unintended systemic biological changes may occur which may increase the risk of chronic diseases, such as osteoporosis. Sex hormones are well known in playing a crucial role in bone acquisition at puberty, 6 and in adulthood, it regulates bone homeostasis.7–9 Therefore, hormone treatments (puberty blockers and GAHT) can affect bone health both in adolescents who undergo puberty suspension and in transgender adults.
Gender affirming hormones, such as estrogen, do cause osteoporosis - that's why women are more prone to osteoporosis than men. Puberty blockers have not been linked to osteoporosis in pre-pubescent patients, despite more than 40 years of use.
GnRH blockers are however dangerous in adults because you need adult level of sex hormones for your bodily function and as such are generally not used for an extended period of time - in pre-pubescent children however it moreso prevents their increase from puberty than it suppresses current levels. This is because GnRH is not produced in significant quantities before puberty, so suppressing it further has far fewer side effects.
They've been used for more than 40 years and few grave side effects have been recorded. It's not a new thing, as I've said, it was and still is fairly common for short kids to be put on GnRH blockers.