The NHS advice is markedly different to New Zealand's Ministry of Health (emphasis added):
"Little is known about the long-term side effects of hormone or puberty blockers in children with gender dysphoria."
"Although the Gender Identity Development Service (GIDS) advises this is a physically reversible treatment if stopped, it is not known what the psychological effects may be."
"It's also not known whether hormone blockers affect the development of the teenage brain or children's bones."
Prior to June, 2020 the NHS described puberty blockers as "full reversible" but no longer does so. See this article for more details.