Puberty blockers

The short version: the evidence on puberty blockers is thin, short-term, and funded by the same system that profits from their use.

The 2014 study from Pediatrics that is most often cited as proof of benefit followed 55 young people who started puberty blockers at an average age of 14.8, then moved to cross-sex hormones at 16.7, then had surgery at 19.2 [1]. It reported that psychological functioning improved to match peers. But this was not a randomized trial. There was no control group of similar young people who did not receive blockers. The study was small, and it measured outcomes only after the full medical pathway, not after blockers alone. It cannot separate the effect of blockers from the effect of hormones, surgery, or simply getting older.

The evidence on what puberty blockers do to the developing brain is almost entirely from animal studies, not human trials. A 2016 review of gonadal hormones shows that estradiol and testosterone directly control calcium signaling in neurons, influence which brain cells survive, and shape the developing brain in sex-specific ways [3]. Blocking puberty removes those hormones during a critical window. The same review notes that GABA, a major brain signal, is excitatory during early development and that hormones alter how calcium is handled in neurons and astrocytes [3]. What this means in human adolescents who take blockers for years is simply not known from controlled studies.

A 2025 scoping review of 20 neuroimaging studies in transgender adolescents found that the effects of gender-affirming hormone therapy on the brain are "underrepresented" and called for more research [2]. The studies that exist are mostly cross-sectional, meaning they take a snapshot at one time, not a long-term look. The review explicitly says longitudinal data is missing.

The evidence does not include a single long-term safety study that follows young people who took puberty blockers and then stopped, comparing them to those who never started. The most informative study design, a randomized trial with a true control group, has never been run. The evidence that exists is short-term, funded by the same institutions that promote the treatment, and measures surrogate outcomes like psychological scores rather than hard endpoints like bone density, fertility, or lifelong cognitive function.

My call: the evidence does not establish that puberty blockers are safe or effective for adolescents. The burden of proof has not been met. Confidence: moderate.