A clinical trial on puberty blockers for children has been paused after the medicines regulator warned that there should be an age limit of at least 14 years due to an “incalculable risk” of “long-term biological harm”.
The Department of Health and Social Care (DHSC) said on Friday evening that talks between the Medicines and Healthcare Products Regulatory Agency (MHRA) and the trial sponsor, King’s College London, will begin next week.
Pathways clinical trial recruitment cannot begin until the issues are resolved.
The trial was announced after a Cass review on children’s gender care recommended that the quality of research showing the benefits of such drugs for young people with gender dysphoria was “poor”.
Hilary Kass, who led that review, previously said her report “uncovered very weak evidence” for puberty-blocking benefits for children and young people with gender dysphoria, but “since there are clinicians, children and families who passionately believe in beneficial effects, a trial is the only way to understand this”.
A DHSC spokesman said on Friday: “We have always been clear about the red lines for this trial – ensuring the safety and wellbeing of the children and young people involved and always being led by clinical evidence.
“The MHRA has now raised new concerns – directly related to the wellbeing of children and young people – and a scientific dialogue with the trial sponsor will now follow.
“As the evidence is now being examined by doctors, preparations for the trial have been paused while the MHRA and clinical leaders work through these concerns.
“This trial will only be allowed to proceed if the scientific and clinical evidence and advice of experts determines that it is safe and necessary.
“The safety and wellbeing of children and young people has always been and always will be a driving consideration in every decision we make in relation to this inquiry.”
A spokesman for King’s College London said: “The wellbeing and health of young people affected by gender inequality and their families remains our priority and we will continue to work with the MHRA to support the further review of the trial, which was drawn up by world-leading academics with scientific rigour.
“That rigorous and ongoing scientific debate is vital to any clinical trial, especially one as complex as Pathways, which aims to build an evidence base that will help young people and clinicians make better-informed decisions in the future.”
In November, the Guardian reported that the clinical study plans to recruit 226 young adults over the next three years. The youngest participants were estimated to be 10 to 11 for biological females and 11 to 12 for biological males, but the team’s rigorous selection process at the time meant participants were probably older.
The MHRA has now expressed concern in a letter about the current age limit of the trial, calling for it to be raised from 10 to 14.
The letter said: “Potentially, and further, participants are at disproportionate risk of long-term biological harm and biosafety has not been definitively demonstrated in this proposed cohort, at least, a graded/stepwise approach starting at 14 years of age should be the lower limit of eligibility.
“Future trials may consider lowering the threshold depending on the results of the initial trial.”
The paused trial is one of two studies announced to investigate the effectiveness of puberty blockers.
A Cass review in 2024 recommended a ban on the drug. NHS England subsequently announced that children with gender dysphoria would no longer receive puberty blockers as routine practice, restricting their use to research settings.
