The UK is Restarting a Puberty Blocker Trial Despite 25 Years of Evidence - Carrie Clark (#4)

Carrie Clark of Genspect UK joins Stella O'Malley and Mia Hughes to scrutinise the NHS Pathways study — a £10 million programme that would enrol children in settings where puberty blockers may be prescribed. Despite the Cass Review finding that the evidence base for blockers was too weak to meet standard paediatric thresholds, the study replicates many of the design failures of the Gender Identity Development Service: no exclusion criteria for autism or mental health, no systematic follow-up of the 9,000 children already treated, and the continued exclusion of detransitioners from the research process.

When the Cass Review reported in April 2024, it found that puberty blockers had been prescribed to children at the Gender Identity Development Service on the basis of evidence so weak it would not meet the standard required in any other area of paediatric medicine. NHS England's response was to announce the Pathways study, a new multi-strand research programme designed to generate the missing evidence. Carrie Clark, Director of Genspect UK, joins Stella O'Malley and Mia Hughes to examine what the programme actually involves and whether it is capable of producing the independent, rigorous findings the Cass Review said were needed. The Pathways study carries a budget of £10 million and will include children in settings where puberty blockers may be prescribed. Clark raises concerns about the study's foundational framing, pointing to language in the research design that reflects gender-identity ideology rather than clinical neutrality. She highlights the absence of meaningful exclusion criteria: children with significant mental health conditions and those on the autism spectrum would not be screened out, despite the Cass Review having documented that co-occurring presentations were inadequately assessed throughout the life of GIDS. Among the most significant issues Clark raises is the NHS's refusal to conduct a systematic follow-up of the 9,000 children who passed through GIDS before it closed. Without longitudinal outcome data on that cohort, any new research programme begins in an evidential void. Researchers cannot establish a baseline understanding of what interventions were applied and what their effects were. The Cass Review explicitly called for this kind of follow-up work; its absence from NHS planning represents a direct failure to act on one of the review's clearest recommendations. The Dutch Protocol, the clinical model on which GIDS and comparable services worldwide were built, receives close examination. Developed in the 1990s from a small, carefully selected patient group, it was never validated at scale. The Cass Review found the underlying Dutch studies to be of poor methodological quality and not generalisable to UK clinical reality. Clark also addresses two studies designed to supply the missing evidence: Tavistock's own Early Intervention Study, whose full results were never published before the service closed, and a major American study led by Joanna Olson-Kennedy whose findings remain inaccessible years after the research was completed. The exclusion of detransitioners from the Pathways study consultation process runs through the episode as a structurally important failure. People who have undergone medical gender transition and subsequently ceased or reversed it represent one of the most direct sources of evidence about real-world outcomes. Their absence from the design process is not easily explained on scientific grounds. Taken alongside the questions about the Dutch Protocol, the missing follow-up cohort and the delayed study results, Clark's analysis raises a difficult question: whether the Pathways study as currently designed is intended to produce genuine knowledge or to provide institutional cover for a course of action already decided.

The dossier behind this episode

The Cass Review: findings and recommendations

The Cass Review was commissioned by NHS England after serious concerns emerged about the capacity, clinical model and evidence base of the national service for children and young people presenting with gender-related distress. For many years, the Tavistock’s Gender Identity Development Service, usually known as GIDS, was the sole national NHS specialist service in England. Referrals rose sharply and the profile of those referred changed substantially, with a marked increase in adolescent girls and young people with complex mental-health, neurodevelopmental and safeguarding needs.

Read the evidence dossier