A contentious UK trial of puberty blockers for children is set to move forward with new age thresholds, sharpening a debate that has already drawn fierce criticism from campaigners who want the study scrapped over concerns about possible harm to young people.
The research was halted in February after the Medicines and Healthcare products Regulatory Agency (MHRA) advised that participants should be at least 14 years old.
Known as Pathways and led by King’s College London (KCL), the UK-wide study was launched late last year after the 2024 Cass Review into children’s gender care called for stronger evidence in the field. That review found that research often cited to support the benefits of puberty blockers for young people with gender dysphoria was of “poor” quality.
Researchers say the trial is designed to answer a central question in a deeply contested area of care: how the timing of treatment may shape quality of life, mental health, physical development, cognitive function and gender-related distress.
The MHRA said it has now approved a “modified protocol” for the trial, alongside what it described as “strengthened safeguards”, including the introduction of minimum entry ages.
KCL researchers said the agreed thresholds mean birth-registered females must be at least 11 years old to participate, while birth-registered males must be at least 12.
That marks a shift from the regulator’s position earlier this year. In a February letter to researchers, the MHRA raised concerns about the trial’s lower age limit and asked for it to be increased to 14.
The letter stated: “Since potentially significant and, as yet, unquantified risk of long-term biological harms is present to participants and biological safety has not been definitively demonstrated in this proposed cohort, at the very least, there should be a graded/stepwise approach starting with those aged 14 as the lower limit of eligibility.”
In an update issued today, the MHRA said it had “sought the advice of independent experts from the Commission on Human Medicines on participant safety and the adequacy of proposed strengthened safeguards”.
Legal action over the study is continuing, with opposition voiced by politicians and public figures including Harry Potter author JK Rowling.
The writer, a prominent critic on gender issues, has described the trial as “an unethical experiment on children who can’t give meaningful consent”.
A campaign group and two individuals are seeking legal action against the Health Research Authority (HRA) and the Department of Health and Social Care, arguing that the trial’s ethical approval process “contained serious flaws”.
Researchers said today that parental consent remains mandatory for every child taking part. They added that young people must also satisfy all other eligibility requirements, including “demonstrating a good understanding of the intervention and its possible benefits and risks”.
The MHRA said no children are expected to be enrolled before 1 August because of the ongoing legal proceedings.
Researchers, from KCL said: “Our priority remains to safely, and robustly, investigate the benefits and risks of puberty suppression for young people with gender incongruence to improve the evidence base and inform NHS healthcare.
“We have worked extensively and openly with the MHRA to understand and resolve the questions they raised about Pathways Trial in February, which were not based on the emergence of any new scientific evidence.
“We have strengthened patient information connected to the trial and introduced a minimum age requirement, however there are no major changes to the design or conduct of Pathways Trial.
“Approval of the modified protocol paves the way for the study to begin, subject to the ongoing judicial review challenge to the MHRA and HRA’s decisions which focuses on their regulatory processes. As a research team we will engage with this fully and openly.”
