Landmark NHS Review Finds 'Remarkably Weak' Evidence for Youth Gender Medicine, Urges Holistic, Cautious Care

The Cass Review

Systematic & evidence reviews Puberty blockers Guidelines & policy

Authors: Hilary Cass
Journal: The Cass Review
Year: 2024
Source: https://segm.org/Final-Cass-Report-2024-NHS-Response-Summary

Summary

The Cass Review was set up after referrals to England's child gender service rose sharply and the patients changed to mostly teenage girls, many with autism or mental health problems. Its final report found that care had rested on 'remarkably weak' evidence. Reviews by the University of York could draw no conclusions on how puberty blockers (drugs that pause puberty) affect gender distress or mental health, and found only limited evidence for hormones. Cass recommended whole-person assessment, standard psychological support, blockers only in a research trial, 'extreme caution' with hormones before 18, national review of every medical case, and regional services. It is the most thorough review of its kind, and later reviews agree the evidence is weak. Its methods are disputed, critics and defenders both have stakes, and some advice rests on judgement rather than data.

Key findings

Set up by NHS England in 2020 and published on 10 April 2024, the 388-page final report makes 32 recommendations for gender services for children and young people in England.
The University of York review of puberty blockers looked at 50 studies (1 high quality, 25 moderate, 24 low). It said no conclusions could be drawn about effects on gender distress, mental health or brain development, and that bone health and height may be harmed.
The York review of cross-sex hormones looked at 53 studies (1 high, 33 moderate, 19 low). It found moderate-quality evidence that mental health may improve during treatment, but no conclusions could be drawn about other effects.
The Review recommends whole-person assessment, including checks for autism and similar conditions and a mental health assessment, with standard, proven talking therapies and medication for distress and other conditions.
Puberty blockers should only be given within a research study (NHS England took a trial forward). Hormones from age 16 need 'extreme caution' and a clear reason for not waiting until 18, and every case for medical treatment should go to a national expert panel.
The Review found that guidelines, including those of WPATH (the World Professional Association for Transgender Health), were not carefully developed. Six of seven NHS adult gender clinics refused to share data for a study of long-term results, and the Review says they should be told to take part.
Families deciding about social transition (new name, clothes or pronouns) for young children should see an experienced clinician early, and all young people should be offered fertility advice and egg or sperm storage before any medical treatment.
The report was criticised by Yale's Integrity Project (McNamara and colleagues, 2024) and in a peer-reviewed paper (Noone and colleagues, 2025). It was defended in Archives of Disease in Childhood (Cheung and colleagues, 2025) and the Journal of Sex & Marital Therapy (McDeavitt and colleagues, 2025).

Abstract

1. The aim of this Review is to make recommendations that ensure that children and young people who are questioning their gender identity or experiencing gender dysphoria receive a high standard of care. Care that meets their needs, is safe, holistic and effective. At its heart are vulnerable children and young people and an NHS service unable to cope with the demand. 2. Yet from the start, the Review stepped into an arena where there were strong and widely divergent opinions unsupported by adequate evidence. The surrounding noise and increasingly toxic, ideological and polarised public debate has made the work of the Review significantly harder and does nothing to serve the children and young people who may already be subject to significant minority stress. 3. Within this context the Review set out to understand the reasons for the growth in referrals and the changing epidemiology, and to identify the clinical approach and service model that would best serve this population. 4. There are conflicting views about the clinical approach, with expectation at times being far from usual clinical practice. This has made some clinicians fearful of working with gender-questioning young people, despite their presentation being similar to many children and young people presenting to other NHS services. 5. Although some think the clinical approach should be based on a social justice model, the NHS works in an evidence-based way. Whilst navigating a way through the surrounding ‘culture war’, the Review has been acutely and increasingly aware of the need for evidence to support its thinking and ultimately the final recommendations made in this report. 6. When the Review started, the evidence base, particularly in relation to the use of puberty blockers and masculinising/feminising hormones, had already been shown to be weak. There was, and remains, a lot of misinformation easily accessible online, with opposing sides of the debate pointing to research to justify a position, regardless of the quality of the studies.

Conclusion

The Cass Review concludes that children and young people questioning their gender identity or experiencing gender dysphoria require a high standard of care that is safe, holistic, and evidence-based. The Review found that the evidence base for medical interventions, particularly puberty blockers and masculinising/feminising hormones, is weak, and that clinical practice has been complicated by a toxic, polarised public debate. The ten key recommendations focus on: (1) ensuring services meet standard NHS care standards with clear clinical leadership; (2) implementing holistic assessment frameworks including screening for neurodevelopmental conditions and mental health; (3) using standard evidence-based psychological and psychopharmacological treatments; (4) ensuring early clinical involvement in decisions about social transition of pre-pubertal children; (5-6) establishing robust research and data collection programmes to improve the evidence base; (7) requiring long-standing gender incongruence as essential but not sufficient for medical treatment; (8) exercising extreme caution in prescribing hormones from age 16; (9) requiring national Multi Disciplinary Team review for all medical treatment cases; and (10) offering fertility counselling and preservation before any medical pathway. The Review emphasises that the NHS must work in an evidence-based way rather than following a social justice model, and that the needs of vulnerable children and young people must be prioritised over ideological positions.

Methodological limitations

Not a guideline or a single review: The report combines research reviews, interviews, NHS data and consultations with clinical judgement. Several recommendations rest on expert judgement rather than comparison data, such as the undefined 'long-standing' gender distress requirement and 'extreme caution' with hormones at 16 and 17.
Disputed way of rating studies: The York reviews used an adapted version of a standard study-quality checklist and only combined moderate- and high-quality studies. Critics say the adapted checklist was untested and differed from the one named in the registered plan (McNamara and colleagues 2024; Noone and colleagues 2025). Supporters reply that adapting checklists is common and the conclusions match other reviews (Cheung and colleagues 2025; McDeavitt and colleagues 2025).
No formal overall rating of certainty: The reviews described the evidence in words and did not formally grade how certain the evidence was for each result. Critics say this made benefits and harms harder to weigh. A later McMaster University review of puberty blockers (2025) did use formal grading and also found the evidence low or very low in certainty.
Leaving out weak studies is debated: Dropping low-quality studies removes possibly biased data but also some evidence. Claims that the Review 'ignored 98% of studies' are wrong, though. Moderate-quality studies (about half of those found) were included, and Cass called the 98% claim 'completely incorrect'.
Reviews rated as biased by critics: Using a standard bias checklist, Noone and colleagues (2025) rated each York review as at high risk of bias. They pointed to unexplained changes from the plan, unclear rules for including studies and studies that were missed. They also argued the Review's own research was held to a lower standard than the studies it judged.
Claimed double standard: The York review of talking therapies also found limited, low-quality evidence. Yet psychological care is recommended first without needing a research study, which critics call a double standard. The Review's view is that psychological support is normal NHS care for distress, not a new treatment.
Some explanations thinly supported: The discussion of why referrals rose and how identity can change (social influences, autism and similar conditions, growing out of gender distress) draws on limited data. Critics call parts of it guesswork, though the Review itself says the causes of the rise are unknown.
Missing long-term data: The planned study of about 9,000 former child patients could not be done because six of seven adult clinics refused to take part. So the Review had no long-term NHS results for the young people it was assessing.
Research searches somewhat dated: The main searches ran to April 2022, with only an informal check of studies up to January 2024. Newer studies were not formally judged.
Disputed expertise: Critics say the Review and York teams lacked clinicians experienced in gender-affirming care. Noone and colleagues later corrected their paper to admit the York team included a former psychologist from the Tavistock child gender clinic. The Review consulted trans adults, detransitioners, families and clinicians, but who was consulted and how much weight each got is not fully clear.
Heavily political on both sides: The report was used to justify the UK ban on puberty blockers and has been cited in US court cases. Cheung and colleagues argue the Yale critique was written mainly to support court cases and was not peer reviewed (checked by other experts). Several authors of the defences are linked to SEGM, a group that urges caution, so both critiques and replies should be weighed with this in mind.
Report itself not peer reviewed: The York research reviews were checked by other experts and published in a medical journal, but the 388-page final report and its recommendations were not.
Built for England: The recommendations are designed for England's NHS and its waiting-list crisis, and may not carry over directly to other health systems.

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Summary

Key findings

Abstract

Conclusion