Amidst growing criticism of the UK’s clinical trial of puberty blockers in children and adolescents with gender distress, a panel of experts met at the House of Lords this month to share their concerns (15 January 2026).
They warned the trial should not go ahead because it would induce harm to otherwise healthy children and would therefore be unethical. They said other important non-pharmaceutical research studies that would not involve giving puberty blockers (PBs) to children should be undertaken instead.
After receiving the go-ahead last November from regulators the Health Research Authority (HRA) and the Medicines Healthcare Products Regulatory Authority (MHRA), the Pathways trial was due to begin recruiting young patients in January.
Its research team, led by King’s College London and the South London and Maudsley NHS Foundation Trust, aim to study the impact of puberty blockers on 226 children and adolescents with gender incongruence. Some will get PBs for 24 months, while others will have to wait for 12 months before receiving them. Outcomes will be compared alongside another group of children with gender distress who will not be given PBs.
But experts agreed that the data linkage study should be given precedence. This would use NHS records to follow 9,000 children previously treated at gender identity services (GIDS) over time, with the aim of gathering evidence on the long-term outcomes, benefits, and harms of PBs. Such a study was recommended by Dr Hilary Cass in her landmark review of gender identity services in April 2024 but was subsequently blocked by adult gender clinics, who refused to provide data.
Michael Biggs, Professor of Sociology at the University of Oxford, St Cross, has been studying outcomes from the prescription of hormones to children with a trans identity since 2018. He told the meeting: “We already know that there are going to be no benefits in the short term (of PBs) — there’s very strong evidence for that. The priority is really publishing the long term outcomes. That is what we need to know about.”
Dr Louise Irvine is co-chair of the Clinical Advisory Network on Sex and Gender (CAN-SG)—a group of UK and Irish clinicians calling for higher standards of evidence based care in gender medicine—and a retired GP as also on the expert panel, agreed that the data linkage study should be prioritised over one that delivers PBs to any children.
“There is a better way forward before exposing children to risky medical experiments,” she said. “We should complete the data linkage study to understand the outcomes of those already treated…we should investigate why referrals have risen so sharply, particularly among teenage girls, and how gender distress is linked to mental health, trauma and neurodiversity.”
Susan Bewley, Professor Emeritus (Honorary), a consultant obstetrician and Professor of Obstetrics and Women’s Health, King’s College, recognised there had been some criticism of the recommended data linkage trial. “The criticism is that it won’t be very useful because the data is very poor. But I don’t think that’s good enough — because poor data is still data.”
She recognised there were several concerns about the Pathways trial, and, under such circumstances, it was normal to address them, she said. In practical terms, it was not impossible, nor unusual, for a trial to be paused.
“I don’t think the ship has sailed,” she said. “The researchers can stop it. They can amend it. They can ask for a revision of the protocol. If there was a misstep in science, we can correct it.”
Dr Sinead Helyar, a clinical researcher and member of the CAN-SG who has worked in clinical trials for over 15 years, listed several other alternative areas of research that could be pursued before resorting to pharmaceutical interventions in children. These included pre-clinical animal experimentation on safety and impacts of PBs during puberty, qualitative studies of the experiences of detransitioners, as well as the full integration of current data, including the safety profile of PBs when used for other clinical populations (e.g. prostate cancer and precocious puberty). “These avenues should be properly explored before any involvement of children to determine effectiveness and safety,” she said.
A major theme explored by the meeting was the trial’s ethical position. Panellists argued that it unethical because it plans to interfere with the normal development of physically healthy children.
“Exposing children to interventions that may permanently alter their development, without solid evidence that they could help, is neither compassionate nor ethical,” said Dr Irvine. “Ethics requires that benefits be clear, substantial and likely—that threshold has not been met”.
Dr Helyar explained that UK clinical trials are governed by national and international codes of ethical conduct and regulation, which demanded that any anticipated benefits justified the risks, and should not be conducted where there is a preceding belief that death or disabling injury will occur.
In addition, she said, UK legislation specifies that clinical trials must be designed so that they minimise any foreseeable risk in relation to a child’s stage of development. But she pointed out: “The Pathways trial, in contrast, proposes to interfere with child development and prevent normal pubertal development, as the key method of investigation. This is in physically healthy children.
“This is a divergence from normal clinical trial practice and of usual risk/benefit analysis of impacts on children who may participate in clinical research,” she said.
The panel also explored the evidence-based systemic harms association with PB use. Dr Helyar listed these as: reduced bone density and early onset osteoporosis, adverse effects on the brain, and concerns around impairment of future sexual functioning and fertility.
It is important to recognise puberty as a fundamental stage of healthy human development, argued Dr Irvine. “It drives sexual maturation, bone growth, fertility, brain development and emotional and social maturation. Suppressing puberty interrupts all of these processes.”
And regarding mental health, she said evidence showed that medical transition does not reduce mental health problems or suicidality. “For the majority of children with gender distress, those feelings resolve through adolescence. Most grow up to be gay or lesbian adults. What these children need is skilled psychological and social support, not medical interventions that permanently alter their development.”
Yet, despite the very serious risks from taking PBs, trial researchers are expected to gain consent from participants and their parents—something the panel viewed as problematic. “Children will be asked to provide assent to this trial – with all the known and probable harms involved,” said Dr Helyar. “How will they have an informed understanding of these harms – which would materialise many years later? In what other circumstance can parents and guardians lawfully consent to such harms to their own children?”
Dr. Irvine agreed: “Neither parents nor children can give valid consent. A child cannot meaningfully assent to the loss of fertility or sexual function because they lack the life experience to understand what those losses mean. Parents cannot ethically consent on their behalf unless they are told the true likelihood that puberty blockers will lead to permanent, life-altering changes.”
The panel also challenged the notion of PBs providing a reversible pause to puberty — something that had been undermined by multiple studies, said Dr Irvine. “The Pathways’ patient information sheet, which I do urge you all to read, treats puberty blockers as though they were a stand alone, reversible, pause. This is misleading. In reality, more than 90% of children with start puberty blockers go on to cross sex hormones.”
With this month marking the start of patient involvement in the trial, the meeting drew attention to its mounting opposition – from clinicians, lawyers and the public.
CAN-SG has published an open letter to health secretary Wes Streeting, stating “grave disquiet” about the trial, which has been signed by 380 UK clinicians. Defending the position of hundreds of clinicians, Dr. Irvine emphasised the gravity of the situation: “This is a child protection issue… and definitely the government should be taking this very, very seriously”.
Other challengers are preparing an urgent judicial review to force the trial to pause, arguing that it constitutes a child protection issue. Claimants include Keira Bell—a detransitioner who famously brought a high profile legal case against GIDS at the Tavistock Centre in London in 2020— and psychotherapist James Esses. They are demanding that recruitment to the trial is stopped and if researchers refuse, they will seek an injunction to stop them.
In addition, there is public petition calling for the trial to be stopped – signed by more than 136,000 people, which is enough to force consideration of a parliamentary debate.