BACKGROUND

In the fall of 2020, the U.K.’s National Institute for Health and Care Excellence (NICE) published initial findings regarding safety and outcomes on the use of puberty blockers and opposite-sex hormones in children and young people diagnosed with gender dysphoria. Because the findings weren’t sufficient to serve as a basis for treatment protocols, England’s National Health Service (NHS) commissioned a review to understand the reasons for the increase in referrals for gender-focused medical intervention and to identify the approach that would best serve the new adolescent population. The review was led by Dr. Hilary Cass, a former president of the Royal College of Pediatricians, England’s equivalent of the American Academy of Pediatrics. Dr. Cass had no prior involvement in this area of medicine and was therefore deemed to be unbiased.

 

The review included:​

• An assessment of all aspects of pediatric gender care services at the Tavistock Clinic’s Gender Identity Development Service (GIDS), the only pediatric gender clinic in operation in the U.K., between 2009 and 2020.​

• Systematic reviews of relevant clinical studies and models of care and outcomes, comparing national and international guidelines and practices.
   

The first findings, The Interim Cass Review, were released in February 2022, followed by the Final Report in April 2024.

 

WHY THE CASS REVIEW WAS COMMISSIONED

The purpose of the Review was to assess current services and to develop a new policy for future treatment of gender dysphoria. Disagreement among clinical professionals had reached a critical point. Some Tavistock pediatric gender therapists had resigned their posts or made formal complaints about how care protocols were influenced by outside activist groups and that puberty blockers  were being prescribed off-label to minors without sufficient time to make a diagnosis and without “informed consent,” the process that provides patients with enough information to understand the implications and consequences of any proposed treatment plan.

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• Parents and advocacy organizations were expressing grave concerns about fast-tracking kids to medicalization.

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• A young woman, Kiera Bell, brought—and won—legal action against GIDS for misdiagnosing her distress as gender dysphoria, resulting in permanent physical harm.

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• There were incredibly long waiting lists due to an exponential increase in adolescents presenting with gender distress and requesting medical intervention.

 

WHAT CASS REVEALED ABOUT U.K. PEDIATRIC GENDER CARE

Teams at GIDS—like their counterparts in U.S. gender clinics—were following guidelines issued by the now-discredited World Professional Association for Transgender Health (WPATH) and the Endocrine Society, based on the Dutch Protocol—practices euphemistically known as “gender-affirming care” and consisting of drugs and surgeries to alleviate mental distress. According to The Cass Review, “in 2011, the U.K. trialled the use of puberty blockers in the ‘early intervention study.’ Preliminary results from that study in 2015-2016 did not demonstrate benefit. The results of the study were not formally published until 2020, at which time it showed there was a lack of any positive measurable outcomes. Despite this, from 2014 puberty blockers moved from a research-only protocol to being available in routine clinical practice and were given to a broader group of patients who would not have met the inclusion criteria of the original protocol.”

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KEY FINDINGS FROM THE CASS REVIEW

• The dramatic rise in numbers of gender dysphoria referrals in teens and young people—predominantly girls and young women—was “a result of a complex interplay between biological, psychological and social factors.”

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• Conflicting views on clinical practices created an atmosphere of fear and confusion, so providers were not always following routine care plans for young people presenting with psychological distress.

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• The systematic evidence review revealed the poor quality of published studies, providing no firm basis for making clinical decisions, or for helping children and families make informed choices. 

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• Strengths and weaknesses of the current evidence base for the care of children and young people were often misrepresented and overstated, in scientific publications, by activist organizations, the mainstream media, and on social media.

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• Controversy took the focus away from the individualized care plans needed.

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• The justification for prescribing puberty blockers was weak, with insufficient proof that they reduce gender dysphoria or improve mental health; blockers impact cognitive and psychosexual development and it is known that they diminish bone density and may limit a child’s height (with other physical impacts unknown).

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• No long-term data is available to understand the impacts of giving opposite-sex hormones to minors.

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• Clinicians had no way to determine in advance which children would continue to suffer from gender dysphoria even when treated with blockers and hormones.

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• Medicalization is not the best path to manage gender-related distress in most young people. For “clinically indicated” cases, efforts should be made to address their wider mental health and psychosocial issues before proceeding down the medical pathway.

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• “Innovation” is needed in the field, but effective oversight is required to avoid unproven approaches being introduced into clinical practice.

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• WPATH, the Endocrine Society, and the authors of studies on pediatric gender medicine engaged in the unethical practice of circular referencing, also known as "citation laundering," in which they reference their own and each other’s policies or findings (without regard for the quality of evidence) to lend legitimacy to claims that would not otherwise withstand scrutiny.

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• Adult gender clinics initially refused to release their data so no conclusions could be drawn regarding the long-term use of hormones. (The refusal speaks volumes.)
   

CHANGES IN THE U.K.

• Closure of GIDS: After the publication of the Interim Cass Report in 2022, the NHS announced that they would be closing the GIDS clinic—this happened in March 2024. By late 2025, a few regional pediatric clinics had opened, with the intention of adopting new, improved clinical protocols.

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• Banning of Puberty Blockers: In advance of The Cass Review, the NHS announced in March 2024 that clinicians should stop routine prescribing of puberty blockers in England and Wales. In December 2024, the new U.K. government headed by the Labour Party (the equivalent of the U.S.’s Democratic Party) imposed an indefinite ban on puberty blockers as a treatment for gender distress. ​(Note: In November 2025, the PATHWAYS Trial, a new and highly controversial trial of puberty blockers led by King’s College London is set to recruit 226 children under 16 with the aim of determining the effects and risks of chemically pausing puberty.)

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• Psychotherapy First: Following the Report’s publication, NHS England published a letter to Hilary Cass—Implementing Advice from The Cass Review—that described how new multi-disciplinary teams would pursue a more holistic approach to treatment, centered on mental health support.

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• Caution on Social Transition in Schools: In December 2023, the U.K. government adjusted their guidance for schools on social transition. They stated that schools “should not proactively initiate action towards a child's social transition.” The Interim Cass Report stated that social transition was “not a neutral act” and recommended great caution. The Final Report unequivocally stated that social transition should be treated with the same caution as prescribing drugs, signaling the end of the common practice of schools unquestioningly using a child’s “chosen” name and whatever pronouns were requested, and letting them use bathrooms and changing rooms based on their “identity” rather than their sex.  In July 2025, new guidance issued by the U.K. Dept. of Education stated that educators should not teach that all people have a gender identity, nor that social transition is a simple solution to feelings of distress or discomfort.

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• Required Professional Training: All staff working with gender-distressed children and teens must undergo a “required professional training curriculum and competencies framework.

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• Follow-Up of GIDS Patients Ordered: Following the Review’s release, the U.K. Health Secretary demanded full co-operation by adult gender clinics (which had previously refused to provide data to researchers). Adult services were required to provide records on trans-identifying patients who started their treatment as children, but might later have changed their minds and/or suffered serious physical and mental health problems as a result. In August 2024, NHS England announced a review led by Dr. David Levy to examine adult services, focusing on safety, patient experience, and service model. The report has not yet been released. 

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• No First Appointments for Minors at AGCs: Adult gender clinics must proceed with extreme caution when offering opposite-sex hormones to young people and no minors can be seen at an AGC.

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• Language Change: Shortly after publication of the Cass Review, the U.K. Health Secretary announced changes to the NHS Constitution to restore the primacy of biological sex. Phrases like “chestfeeding” and “people with ovaries” will no longer be used. Biologically precise, sex-based language that better describes the medical needs of all patients were to be reinstated—but these updates have not yet been published.

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• Same-Sex Medical Staff for Intimate Care: Patients in England can request a doctor of the same sex for intimate care under proposed changes to the NHS constitution. This is  not statutory law but patients have the right to request a same sex clinician and, wherever possible, one should be provided.

 

RELATED RESOURCES​

FAIR: After Cass (YouTube Video)

 

WBUR: Interview with Dr. Hilary Cass 

 

Gender Medicine in the U.S.: How the Cass Review Failed To Land, Jennifer Block, The British Medical Journal, May 2024