The facts
Medical risks
What puberty blockers, hormones and surgeries do exactly — and what stays if you later want to turn back. No propaganda in either direction. Just facts you don't easily find together anywhere else.
Puberty blockers — not a pause button
The message children and parents are told: "it's safe, you can come off them, it gives time to think." That isn't true.
98% proceed to hormones. Among Dutch and British children who started puberty blockers, research showed up to 98% proceeded to cross-sex hormones. For those who don't get blockers? It's about 15-20%. Blockers change the path.
Bone growth is halted. Bone density decreases during use. With long-term use (1-3 years), it's unclear to what extent it recovers. Risk of osteoporosis later in life is elevated.
Brain development. Puberty is also the period in which the brain is hormonally shaped. Research in sheep and humans suggests that puberty blockers affect cognitive and emotional development — how much exactly is unknown because there are no long-term studies.
Sexual function. In boys who get blockers before puberty, the genitals never fully develop — which severely limits later surgical techniques and sexual function.
Fertility. The combination of blockers and subsequent cross-sex hormones often leads to permanent infertility. Pre-pubertal children cannot freeze eggs or sperm because they don't exist yet.
The Cass Review (2024) concluded that the evidence for the claim "blockers give time to think" is remarkably weak. Not a single randomised study. No long-term data on psychological outcomes. The NHS stopped routine prescription.
Testosterone in girls and women
In girls and women who take testosterone to appear more masculine:
Irreversible: deeper voice (within 3-12 months, permanent); facial and body hair (permanent); clitoral enlargement (permanent); enlargement of the vocal cords; male-pattern hair loss; changes in smell and sweat.
Possibly reversible: menstruation stops (sometimes returns after stopping); muscle mass increase; fat redistribution; libido changes; mood changes.
Health: elevated risk of cardiovascular disease (LDL up, HDL down); liver strain; red blood cells up (thickens the blood, risk of thrombosis); insulin sensitivity drops; atrophy of vaginal tissue (thinner, more painful).
Fertility: menstruation usually stops, but pregnancy remains possible — dangerous because testosterone is harmful to a foetus. The effect on long-term fertility after stopping is unclear.
Oestrogen and anti-androgens in boys and men
In boys and men who take oestrogen (often combined with testosterone blockers):
Irreversible: breast growth (permanent, requires mastectomy to remove); shrinkage of testicles (often permanent); permanent reduction or loss of fertility; reduction or loss of spontaneous erections.
Possibly reversible: fat redistribution (hips, thighs, face); reduced muscle mass; softer skin; less body hair.
Not changeable by hormones: voice (stays masculine unless surgically altered); height; skull shape; shoulder width; hands and feet.
Health: elevated risk of thrombosis (pulmonary embolism, stroke) — especially in smokers and over 40. Increased risk of breast cancer. Gallstones. Mood change, sometimes depression.
Sexual function: reduced libido (in 70-90%), erectile dysfunction, anorgasmia. For some men this passes over time — for others it's permanent.
What we don't know
Perhaps the most important point: the long-term consequences haven't been studied. The medical transition of young people as it now takes place — blockers at 12, hormones at 16, surgeries at 18-25 — has only existed at this scale since around 2010.
We don't know how lifelong testosterone use in women turns out at age 60. We don't know what lasting oestrogen exposure does in men on a 50-year horizon. We don't know how many people regret transition after fifteen years — the existing studies have a much shorter follow-up and high dropout (people who regret tend to disappear from care and from the statistics).
The Cass Review called this weak evidence. Sweden, Finland, Denmark, Norway and the United Kingdom have tightened their protocols. The Netherlands is alone in continuing on the old path.