Dr Hilary Cass says ‘more children will be harmed’ without puberty blockers trial
Dr Hilary Cass spoke on the BBC over the weekend. (BBC/YouTube)
Dr Hilary Cass spoke on the BBC over the weekend. (Image: BBC/YouTube)
Dr Hilary Cass has defended the NHS-backed Pathways puberty blockers trial as a harm-reduction measure, saying she is “absolutely convinced that more children will be harmed if we don’t do the trial than if we do”.
Cass made the comments in a BBC interview, as the study faces political pressure and a legal challenge calling for it to be scrapped.
The Pathways clinical trial, which confirmed the minimum ages for young participants, will be run by researchers at Kings College London (KCL). Researchers plan to examine the impact of puberty blockers on participants’ physical, social and emotional wellbeing, such as bone density, brain function and fertility.
Cass claimed that since UK-wide restrictions were introduced, “some of the hype about risks have been exaggerated in that we genuinely don’t know if there are harms”.
She described the trial as “essential” to answer whether the drugs are helpful, adding that young people will be “closely monitored in every respect” and that the drugs would be stopped if concerns emerge.
Cass also claimed that, without a regulated trial, young people would continue to access medication through “unregulated and dangerous routes”.
She said: “Today we have young people turning up in the clinics on testosterone at 11, which we know is irreversible,” adding that puberty blockers might give more time for therapeutic support. Previous guidance said testosterone should not be prescribed in the UK for children under 16 seeking gender treatment.
Pathways trial timeline and safeguards
The research was recommended after Cass’s 2024 review of children’s gender medicine, which suggested weak evidence behind puberty blockers’ use. In 2024, the government brought in a UK-wide, indefinite ban on puberty blockers being prescribed privately or through the NHS for children’s gender care.
The trial was announced in November 2025 before being paused in February of this year when medical regulators proposed a minimum age of 14 for participation. KCL researchers later agreed minimum ages of 11 for trans male participants and 12 for trans female participants. It’s understood the trial will start in August, subject to ongoing legal action.
Political and legal pressure
Health Secretary James Murray told Parliament on Monday: “I have felt uncomfortable and uneasy about some of the challenges raised by this matter.” He added: “But for me, following the clinical advice, basing future decisions on clinical evidence, is the right way to move forward in the context of me having received the most robust assurances about the safeguards which are in place to protect young people involved in this trial from receiving harm.”
Campaigners bringing legal action argue the trial is unethical, saying children can’t give properly informed consent to take part. TransActual’s healthcare director Chay Brown welcomed the trial, but said the NHS should reverse the puberty blocker ban and “provide timely and holistic care for all trans people on the basis of informed consent – not the latest moral panic”.
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