A Cautious Endorsement of the Cass Review

The British Medical Association accepts the Cass Review methodology but questions its recommendations

Photo by Etactics Inc on Unsplash

The final report of the Cass Review of gender identity services for children and young people in the United Kingdom was a turning point in the debate on pediatric medical transition both in the United Kingdom and internationally. The recommendations of the final report received bipartisan support and the government has introduced tight restrictions on the use of puberty blockers and cross-sex hormones for patients under the age of 16.

The review also attracted considerable opposition. One high profile rejection of the review came from the council of the British Medical Association which adopted a resolution rejecting the conclusions of the Cass Review. This resolution, in turn, created controversy. The BMA is a trade union which represents doctors and medical students in the United Kingdom. In the past, it has avoided taking positions on matters relating to the actual practice of medicine. As a result of widespread opposition from its members, the council adopted a neutral position on the Cass Review and appointed a committee to prepare a critique of the final report. The report of this committee (the “Critique”) found that the methodology of the Cass Review was sound but expressed disagreement over the implementation of the recommendations of the Review. The Critique was prepared by a committee described as the Task and Finish Group. The members of this group are not named, but they included both supporters and critics of the gender-affirming model of care.

Evaluation of the Evidence

The Cass Review has been the subject of considerable criticism, including a grey-literature response by McNamara et al. and a peer-reviewed article by Noone et al. These critiques received detailed responses in peer reviewed articles by Cheung et al., McDeavitt et al., al., and Kingdon et al. The BMA Critique did not address these articles and, instead, relied on an independent assessment of the Cass Review.

Many of the early critics of the Cass Review focussed on the methodology of the systematic reviews conducted by the University of York (the Taylor et al. reviews). The BMA’s approach was to commission Health Economics and Outcomes Research Ltd (HEOR) to conduct a re-appraisal of the studies in the systematic reviews.

The Taylor et al. review used a modified version of the Newcastle-Ottawa Scale to assess risk of bias in the studies of puberty blockers and cross-sex hormones. The HEOR group recommended a modified National Heart, Lung, and Blood Institute (NHLBI) Study Quality Assessment Tool. The Executive Summary describes the outcome as follows:

These analyses reassessed the Taylor et al systematic reviews and supported their findings that the evidence base for puberty suppression and gender affirming hormones is limited, predominantly observational, and characterised by substantial uncertainty. They found no evidence that the Taylor et al. systematic reviews that were commissioned by and informed the Cass Review on puberty blockers and hormones, missed or excluded any high-quality studies, nor that the Taylor reviewers were biased in how studies were rated or synthesised. They also highlighted that there was limited evidence of harm of treatment. HEOR’s analysis suggested that this uncertainty is symmetrical: signals of both benefit and harm are present, but neither can be quantified with high confidence.

HEOR also examined the treatment impact statements in the Cass Review to determine whether they were substantiated by the cited evidence. They found that out of 28 statements, 15 were fully substantiated, 10 were partially substantiated and 3 were not substantiated. None of the statements rated as unsubstantiated invalidated the main conclusions of the Cass Review.

Structured interviews were conducted with the stakeholder groups that had contributed to to the Cass Review to assess whether the consultation process was adequate. The groups that participated in the BMA consultation were Mermaids, the LGBT Foundation, The Proud Trust and The Kite Trust. The Bayswater Support Group, which was the only group that supported tighter regulation of pediatric medical transition, declined to participate. The Critique concluded that the Cass Review met the current standards in the U.K. for stakeholder consultation except for timeliness. All the stakeholders who responded complained that they were engaged too late in the process.

The BMA Critique subjected the Cass Review to much more detailed scrutiny than normal peer review or anything that has been applied to the WPATH Standards of Care or any other document supporting the affirming model of care. No overriding errors were identified. This should be the final answer to claims that the Cass Review has been “debunked.”

Consensus and Disagreement

The Task and Finish Group identified seven areas of consensus and seven areas of disagreement. The areas of consensus were:

1. The evidence base for puberty suppression and gender affirming hormones in adolescents is limited;

2. There is substantial uncertainty regarding both long term benefits and long-term harms;

3. There was a need to improve evidence generation which should prioritise the use of existing data (e.g. a data linkage study);

4. Children and young people presenting with gender-related distress often have complex clinical profiles and require care which is holistic, multidisciplinary and developmentally informed;

5. The service model should move away from a single centre to regional multidisciplinary services;

6. Shared decision making must balance principles of beneficence, non-maleficence, respect for autonomy and the child’s right to an open future; and

7. Prescribing decisions must be made in the context of limited evidence of long-term benefit, known adverse effects and plausible long term risks and absence of reliable predictors of individual outcomes.

There was disagreement on the emphasis to be given to the various factors listed in points 6 and 7 and this led to the areas of disagreement. There were seven areas in which the Task and Finish Group divided into two views. There were 4 members of the group who favoured what the Critique calls “View A”, 6 who favoured “View B” and 2 who declared no position. The areas of disagreement were classified as follows:

1. Interpretation of the evidence base:

a. The absence of robust evidence of benefit combined with known and plausible harms supports a precautionary stance.

b. The same limitations that constrain inference about benefit also constrain inference about harm and absence of high-quality evidence is not evidence of absence of benefit, and is not sufficient grounds to restrict treatment.

2. Role of interpretive bias and framing:

a. The Cass Review broadly reflects the literature and appropriately emphasises uncertainty and potential risks.

b. Evidence evaluation is shaped by positionality and the Cass Review may over-emphasise potential harms and under-represent reported benefits.

3. Scope of the evaluation and inclusion of evidence types in the Cass Review:

a. The focus on clinical studies and stakeholder engagement is appropriate for a scientific evaluation.

b. There was insufficient consideration of experiential evidence.

4. Stakeholder engagement process:

a. The Cass Review’s engagement with lived experience was broadly in line with standards at the time for a consultation exercise. Healthcare choices are not the same as consumer choice and the principle of co-production in healthcare policy does not confer a right to receive non-beneficial treatments.

b. Stakeholders expressed concern that they were not being listened to. The review should have been conducted according to the standards of co-production.

5. Access to puberty blockers and hormones:

a. Given the low certainty of evidence, known adverse effects and potential for harm, restriction of routine prescribing is justified.

b. Restrictions of access are associated with harm (e.g. worsening of distress, loss of therapeutic window) and treatment should remain available within a regulated, multidisciplinary framework with informed consent and monitoring.

6. Treating individuals in realms of uncertainty:

a. Removal of access to gender affirming treatment is not known to be associated with harm.

b. The removal of access is associated with known harm and access to treatment after shared decision-making is justified.

7. Implications for BMA positioning:

a. The BMA should support the recommendation of the Cass Review to carry out a “data-linkage” study of long-term health outcomes of children and young people treated at the Tavistock Clinic, but there are ethical concerns about commencing further interventional studies such as the PATHWAYS puberty blockers trial.

b. The BMA should avoid any position that may be interpreted as endorsing the Cass Review in full.

The BMA Critique provides a fair summary of opposing views on some of the key issues in pediatric gender medicine. The Task and Finish Group did excellent work in bringing doctors with widely differing perspectives together. However, the very fact that a discussion of diverse views, which would be routine in most areas of medicine, seems like a breakthrough in the debate on pediatric gender medicine shows just how far gender medicine has strayed from ordinary scientific and clinical standards.

Implementation of the Cass Review

The BMA Critique does not have any concerns over the implementation of some of the recommendations of the Cass Review, such as the establishment of regional services for gender-distressed children and young people, but does object that the restrictions on the prescription of puberty blockers goes beyond what the Cass Review recommended.

Just before the final report of the Cass Review was published, NHS England issued a new clinical policy which ended routine prescription of puberty blockers for gender dysphoria. In December 2024, the government extended this ban to private providers. There is an exception for research trials, but to date, no research trial has been approved. Although not mentioned in the BMA Critique, in March, 2026 NHS England paused prescriptions of cross-sex hormones for patients under the age of 18.

In the UK, puberty blockers for gender dysphoria in children are prescribed “off-label,” that is, without regulatory approval for that indication. Prescribing decisions are governed by physician judgment within a regulatory framework. According to the BMA Critique, the decision to impose statutory restrictions on prescribing for a specific indication “departs from usual UK clinical practice” and “represents a significant escalation.”

The Exceptionalism of Gender Medicine

What the BMA Critique fails to acknowledge is that the entire field of gender medicine departs from usual clinical practice. The Health and Human Services Review identified three factors that make gender medicine exceptional. All three are found in other areas of medicine, but the combination of the three in gender medicine gives rise to exceptionalism that justifies an exceptional policy response.

The first is that the diagnosis of gender dysphoria is entirely dependent on self-reported symptoms, which the clinician must assess subjectively. There is no blood test or scan that can confirm whether a young patient is experiencing gender dysphoria, which is likely to persist, or some other condition. This is, of course, inevitable in all psychiatric conditions, but the diagnosis of gender dysphoria is complicated by the fact that it depends, in part, on culture-bound stereotypes of gender roles. Gender dysphoria is frequently associated with other mental health or neurodevelopmental conditions, which adds another layer of complexity to diagnosis. Furthermore, laws and policies against “conversion therapy” deter mental health professionals from doing adequate exploratory work with gender distressed children and young people.

The second exceptional factor is the poor understanding of the natural course of gender dysphoria. The starting point for any treatment decision is an understanding of the natural course of a condition in the absence of treatment. In the case of gender dysphoria, all the studies prior to around 2015 found that childhood onset gender dysphoria resolved during puberty in anywhere from 65 to 95 percent of cases and was often a precursor to same-sex attraction. There is no research on the natural course of gender dysphoria in the new, predominantly female cohort of adolescent onset patients.

The third exceptional factor is that the treatments for gender dysphoria are invasive and highly risky. Known risks of hormones and puberty blockers include sterility, reduced bone density, interference with cognitive development and increased risk of cardiovascular disease. Systematic reviews have found most of the evidence for these risks to be of low certainty. This has led some clinicians to argue that where the evidence for risks and benefits is of both low certainty, treatment decisions should be made through shared decision making with more weight given to patient values and preferences. The counterargument, which is elaborated on in the HHS Review, is that the evidence of benefit and harm is not symmetrical. Systematic reviews will not provide adequate evidence on harms because most clinical studies have too short a follow-up period and too small a population to detect serious harms. For example, the effects of puberty blockers on bone density may not become apparent until after the age of 30 when bone density begins to decline. For this reason, assessment of potential harm needs to consider other forms of evidence such as studies of the effects of a treatment in other conditions, animal studies and inferences from basic science and physiology. All this evidence points to the risk of serious harm from puberty blockers and cross-sex hormones.

The HHS Review points out that none of these factors, by themselves, are unique to gender medicine. There are many conditions which are diagnosed through self-reported symptoms. Minor ailments, which resolve naturally, may be treated to relieve discomfort. High-risk treatments may be employed in conditions which would be fatal if left untreated. However, only in gender medicine are invasive treatments employed for a condition which has only subjective diagnostic criteria and a natural course which tends towards resolution.

The exceptional nature of pediatric gender medicine demands a cautious approach at the clinical level. There are two additional factors which justify the escalation to legal controls.

The first is the abandonment of sound clinical practice in pediatric gender medicine. The Cass Review was commissioned because of concerns raised by clinicians working at the youth gender identity service at the Tavistock Clinic. The failure of the clinic management to address these concerns led to the closure of the clinic. Patients were being prescribed hormones and puberty blockers with minimal assessment; co-morbid mental health conditions were ignored and follow up was inadequate. Reluctant parents were frightened into compliance by exploiting the fear of suicide. The HHS Review found whistleblower reports of similar problems in US clinics and reports from concerned parents and detransitioners show that the same problems exist in private clinics and worldwide.

The second exceptional factor is the politicization of the debate on pediatric gender medicine. The BMA Critique suggests that health care policies should be developed through a process of co-production in which stakeholder groups such as Mermaids Gender. However, it fails to realise that pressure by these stakeholder groups was the source of many of the problems that the Cass Review was set up to investigate. The undue influence exercised by Mermaids Gender and other transgender charities on policies in the Tavistock Clinic was documented by Hannah Barnes in her 2023 book Time to Think: The Inside Story of the Collapse of the Tavistock’s Gender Service for Children. Transgender activists have framed access to medical transition as a human rights issue and are indifferent to or actively hostile to evidence-based medicine. This problem is also worldwide and has spread to universities, academic journals and major medical and mental health organizations.

There has been a catastrophic failure of the chain of trust in gender medicine at all levels. The Standards of Care of the World Professional Association for Transgender Health, which are the basis for the positions taken by almost all medical and mental health organizations, have been exposed as untrustworthy. The Cass Review found that the WPATH guidelines were of low quality. Disclosures in litigation in the United States revealed the extent to which the guidelines were politically influenced. Medical journals routinely publish research of questionable quality when it endorses gender affirming care but resist the publication of criticism and corrections. Presentations by critics of the gender-affirming model at medical societies are met by demands for cancellation and protests.

There are some encouraging signs. The American Society of Plastic Surgeons recently adopted a recommendation to delay gender affirming surgery until the age of 19. The fact that the BMA itself was able to bring doctors from both sides of the debate together on a single committee is a step forward. However, the fact that the names of the committee members have not been disclosed suggests that there is still a long way to go in restoring conditions for normal scientific debate. These are very small steps to resolving a very large problem. Vulnerable young people are still being harmed and escalation of legal action to protect them is justified.