Britain’s biggest doctors’ union drops opposition to Cass Review - but still backs puberty blockers

Britain's biggest doctors’ union has backed down in the row over child gender medicine after admitting the evidence behind prescribing puberty blockers and cross-sex hormones for children is marked by “substantial uncertainty”.

The British Medical Association - which previously voted to “oppose the implementation” of the Cass Review - today accepted that much of Baroness Dr Hilary Cass’s landmark report is supported by evidence.

However the doctors’ union believes medics should still have the autonomy to prescribe puberty blockers.

Professor David Strain, chair of the BMA’s board of science and lead author of the union’s new report, said in an interview today: “The baroness has been vindicated in the way she approached the data.”

In July 2024 the BMA’s council voted to “oppose implementation" of the Cass review which called for an overhaul of NHS gender services and a move away from a “medical pathway” that had led to thousands of children being prescribed powerful sex hormone drugs. It said at that time the recommendations were “unsubstantiated,” and called for her recommendations to be “paused” until it had conducted its own review.

The BMA today published its long-awaited review of this report.

Its findings state “the evidence base for puberty blockers and gender affirming hormones is limited and characterised by substantial uncertainty in both benefits and harms”.

The BMA report also backs calls for “improved research, better data, and more robust multidisciplinary services”.

Asked in a previous interview to name a single one of Cass’s 32 recommendations that the BMA opposed, Professor Strain replied: “I can’t.”

He added: “She approached an area of significant uncertainty with that prime rule of medicine, of ‘first, do no harm’.”

The Cass Review, commissioned by NHS England and published last year, examined evidence from gender identity services and data relating to 113,000 children.

Following the review, NHS England stopped routinely prescribing puberty blockers to children outside clinical trials.

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The government later introduced legislation banning their use for under-18s.

Puberty blockers suppress physical changes linked to puberty, including breast development, periods and facial hair. Critics say the longer term benefits have not been shown in medical evidence.

Cass warned there were concerns about potential impacts on fertility, bone health and brain development, as well as major gaps in the evidence base surrounding treatment.

The BMA’s new report says much of the Cass Review “is backed up by the research it references”.

However, it also argues that some conclusions “don't fully reflect the complexities” of caring for people who feel their gender is different to the sex they were assigned to at birth - and are only partly supported, or not supported at all, by the evidence”.

The report adds that there was sometimes “a tendency for statements to simplify complex findings or to emphasise potential risks without also outlining possible benefits”.

The union also criticised the way the Cass Review had been implemented, including delays in setting up new NHS services.

Prof Strain said the government’s decision to ban puberty blockers was an “overreach”.

He said: “We are continuing to oppose a ban on puberty blockers for several reasons, not least because it is a threat to the autonomy of a doctor.

“We spend decades training on how to use drugs, and to have a political decision affecting the way we prescribe is wrong.”

He said “appropriately trained specialists” working within new NHS gender clinics should still be able to prescribe puberty blockers and gender-affirming hormones within a research framework.

But he added: “We are not advocating that these drugs [puberty blockers] should be freely available.”

The BMA report reveals divisions within the union over puberty blockers.

A 12-member “task and finish group” spent almost two years examining the Cass findings.

According to the report, four members supported restrictions on puberty blockers because of their “known and plausible harms”.

Six supported continued NHS access and argued the Cass Review may “over-emphasis potential harms and under-represent reported benefits”.

Two members were neutral.

The report also includes criticism from some contributors to the Cass Review process, with concerns that transgender advocacy groups were engaged too late and that some participants did not feel fully represented in the final conclusions.

The publication of the BMA report is likely to reignite arguments over the treatment of children experiencing gender distress.