Thank you for your respectfully worded question/comment. While some of the side effects of hormones are known (possible loss of head hair, cardiovascular risks, for example), neither puberty blocking hormones, nor testosterone, have been adequately studied in this population. WPATH acknowledges this dearth of data here (page 11). Researchers should be recruiting for longitudinal, long-term studies now but I don’t see any indication of that.

I’ll also use your question to say something about WPATH in general. I am aware of WPATH standards. But here are some of my concerns:

• Increasingly, at least in the US, transactivists are pushing for “informed consent” – even for minors – in lieu of WPATH procedures. These activists consider the requirements to see a therapist, “prove” one’s intention of changing genders, and be on hormones for several years before moving onto surgery to be unnecessary “gatekeeping.” So there is pressure to make those standards weaker and to accelerate medical transition for those who ask for it.
  

• Even WPATH itself acknowledges (again, page 11, at this link) only a small number of gender dysphoric children (between 6-27%)  go on to be gender dysphoric adults. So I question the entire premise underlying the standard transgender protocol, particularly as it applies to children and adolescents.