Campaigners have launched legal action to halt a new NHS-funded clinical trial on puberty blockers, arguing the research could put vulnerable children at risk. The move intensifies a national debate over gender medicine in the UK, coming months after the Cass Review concluded that evidence supporting puberty blocker treatment was “remarkably weak” and based on “shaky foundations”.
The planned study, known as the Pathways trial, was developed in response to the Cass Review’s call for stronger research into treatments for gender-questioning young people. Yet campaigners say the trial itself threatens the welfare of participants, warning that puberty blockers may cause irreversible harms, including potential long-term effects on fertility.
The legal letters were sent to the Medicines and Healthcare products Regulatory Agency (MHRA) and the Health Research Authority (HRA), and copied to Health Secretary Wes Streeting and NHS England. The challenge is led by the Bayswater Support Group — a parent collective — alongside psychotherapist James Esses and Keira Bell, the detransitioner who previously brought a landmark case over care at the Tavistock Centre.
They argue the trial “fails to safeguard the rights, safety and wellbeing” of minors, describing the participants as a highly vulnerable group. They also question why drug treatments are being prioritised when counselling and psychological support have shown benefits for many children experiencing gender distress.
How the trial will operate
The Pathways trial, run by researchers at King’s College London, is due to begin in January and aims to recruit around 226 children over three years. The youngest eligible participants would be 10 to 11 for biological girls and 11 to 12 for boys, with an upper age limit of just under 16.
One cohort will receive puberty blockers immediately for two years, while another group will start the drugs after a one-year delay. Results are expected within four years. The HRA said the study has “all the necessary regulatory approvals” required to begin.
Concerns raised by past experiences
Bell, who was prescribed blockers as a teenager before later detransitioning, said the treatment left her “angry” and unaware of its impact on brain and emotional development. She questioned why the NHS has not built a research programme based on the experiences of those who previously received puberty blockers. “There are children who have already been down this pathway. I’m one of them,” she said.
Her earlier legal case against the Tavistock clinic triggered major reforms, including the closure of the service and the creation of new regional gender hubs with stricter safeguarding rules.
Government says trial is needed to rebuild evidence base
Health Secretary Wes Streeting has defended the research, saying it will help the NHS develop an evidence-backed approach to treating young people with gender incongruence. In a statement to parliament last month, he acknowledged significant concerns around safety, efficacy and consent, but noted that strict eligibility rules, clinical review processes and parental approval are required.
Legal expert Professor Jonathan Montgomery, who advised the research team, said the trial reflects improved safeguarding within the NHS’s new gender services. He argued that stopping research altogether would be detrimental. “Young people and their families have been let down by a collective failure to generate the science needed for informed decisions,” he said. “Blocking research would compound that failure.”
Gender medicine under national scrutiny
The Cass Review, published last year, led to the NHS banning the routine prescription of puberty blockers for gender dysphoria and calling for robust clinical trials. Since then, gender care has become one of the most sensitive issues in UK health policy, with ministers under pressure to ensure that any future treatments are grounded in strong scientific evidence. The new trial represents the first large-scale attempt to address longstanding gaps in data — but now faces a high-profile legal battle before it even begins.
