A new UK clinical trial will assess the risks and benefits of puberty-blocking drugs for children experiencing gender distress, following last year’s nationwide ban on their routine use.
The trial, led by researchers at King’s College London (KCL), aims to provide robust evidence on the controversial treatment, which the Cass Review previously found lacked sufficient clinical data to justify use in under-18s.
Around 220 children under 16 who have reached puberty and have a diagnosis of gender incongruence will take part in the study.
They must meet strict medical and psychological criteria, receive detailed assessments, and demonstrate an informed understanding of the treatment’s potential effects. Their parents or guardians must also give consent.
Study lead Prof Emily Simonoff said many families attending gender services do not know what to do given the uncertainty surrounding puberty blockers.
She said the trial will not seek a universal conclusion but will balance potential mental-health benefits against physical and developmental risks. It will also be the first study to closely examine the drugs’ effects on brain development.
Participants will be randomly divided into two groups—one starting treatment immediately and the other after 12 months. Researchers will monitor bone density, brain development, mental health and overall wellbeing.
Ethical approval has already been granted, and recruitment is expected to begin in January, with initial results due in about four years.
A separate observational study will track 3,000 children receiving other forms of support.
The trial has sparked heated debate. Campaigners, including Keira Bell whose legal challenge against puberty blockers drew national attention argue the study is unethical and threatens further legal action. Some clinicians have also raised concerns.
However, Dr Hilary Cass, who led the landmark review prompting the ban, welcomed the research, saying a formal trial was the only way forward to resolve disagreements about the drugs’ effects.
LGBTQ+ rights, charity Stonewall urged policymakers to ensure young people receive high-quality, evidence-based care informed by their lived experiences.
