Though puberty bockers have a significant history of usage, they are only technically approved by the FDA for treating children who begin puberty too early and have not been approved for treating transgender children.
Additionally, there has been little research done on children who take the medication for extended periods of time, etc. One study found that puberty blockers can result in a decrease in bone density, though researchers are unsure if this decrease can be reversed once the child stops taking puberty blockers. Initial studies seem to suggest that starting estrogen or testosterone can help regain bone density, but are inconclusive on whether they can fully reverse the damage done. Another issue is that we don’t know how much pubertal hormones impact brain development in adolescence.
Hormone treatments (such as transgender girls taking estrogen) also pose their own risks. Patients who undergo hormone treatment may be at higher risk of developing heart disease, diabetes, and blood clots in the future. Hormone treatments can also reduce fertility. In response to this risk, many adults store their eggs or sperm before starting hormone treatments. However, transgender children may be too young for that process, so they do not have that “back-up plan” in the case that they are rendered infertile.
Though these risks are often taken by informed adult patients, since they are not overwhelmingly high, allowing children to take these risks is a completely different story. For instance, we allow adults to drink alcohol and smoke cigarettes knowing that there are high risks associated with these behaviors, but we would never let children take those same risks. In a similar way, even though transgender adults make take on the risks associated with medical transition, transgender children should not be allowed to take those risks because they cannot be expected to understand what those risks entail and they are not cognitively developed enough to make that decision.