The UK is Restarting a Puberty Blocker Trial Despite 25 Years of Evidence - Carrie Clark (#4)
13 March 2025
With Carrie Clark
UK
The Cass Review exposed deep failings in NHS gender services for children, yet the NHS is now designing a new £10 million puberty blocker trial — the Pathways study. Carrie Clark of Genspect UK examines the study's methodological gaps, the absence of mental health exclusion criteria, the buried Tavistock Early Intervention Study, and the NHS's refusal to follow up on the 9,000 children who passed through the now-closed GIDS clinic.
The Cass Review, published in April 2024, was the most thorough independent examination of NHS gender services for children ever conducted in the United Kingdom. Its conclusions were unambiguous: the evidence base for puberty blocker treatment was weak, the Tavistock clinic's Gender Identity Development Service had operated without adequate clinical oversight, and thousands of children had been treated under a protocol whose long-term outcomes remained largely unknown. Against that backdrop, news that the NHS is designing a new clinical trial — the Pathways study — to investigate puberty blockers in minors has drawn sharp criticism from researchers and patient advocates. Carrie Clark, Director of Genspect UK, joins Stella O'Malley and Mia Hughes to scrutinise the proposed trial in detail. Genspect supports families navigating gender distress through evidence-based, non-medicalising approaches, and Clark has followed the Pathways study's design and consultation process closely. Her central argument is that the proposed research risks repeating the methodological failures of its predecessors rather than correcting them, and that a key stakeholder group — people who have detransitioned — has been excluded from shaping the research framework. The Pathways study is a £10 million programme structured across four strands, intended to generate the evidence base that, Clark argues, should have been required before puberty blockers were prescribed to thousands of children at GIDS. She identifies significant structural problems in its design: there are no exclusion criteria relating to co-occurring mental health conditions or autism, populations substantially over-represented among former GIDS patients. The study also relies heavily on self-reported outcomes, a methodology identified as a source of considerable bias in earlier research in this field. The episode traces the study's scientific lineage back to the Dutch Protocol — the framework developed in the Netherlands in the 1990s that became the international template for paediatric gender medicine. Clark outlines its methodological limitations: a small, carefully selected patient group whose results were subsequently applied to a far broader and more complex population than the original study ever examined. Tavistock's own Early Intervention Study, which gathered longitudinal data alongside clinical services at GIDS, produced results that were never fully published, leaving a substantial gap in the formal evidence record. Also examined is the NHS's decision not to conduct systematic follow-up with the approximately 9,000 children who passed through GIDS before the clinic closed. Their outcomes — whether positive, negative, or neutral — remain formally undocumented. The exclusion of detransitioned people from the Pathways consultation process compounds this deficit, removing from the study's design the one perspective best placed to inform a rigorous safety evaluation. These issues together raise a pointed question about whether the Pathways study represents the genuine evidence-based reset that the Cass Review called for, or whether it replicates the institutional patterns that made such a review necessary in the first place.
