The NHS will begin recruiting children as young as 11 for its puberty blocker trial from August despite Britain’s medicines regulator previously warning of “potentially significant” long-term biological harms.
King’s College London, which is leading the NHS Pathways study, confirmed it had reached agreement with the Medicines and Healthcare products Regulatory Agency (MHRA) on revised trial protocols.
Under the updated rules, girls aged 11 and above and boys aged 12 and above will be eligible to take part in the study.
Previously, there was no minimum age requirement, although the MHRA had proposed introducing a threshold of 14.
The trial was suspended indefinitely in February after the MHRA raised concerns about the potential risks facing children enrolled in the research.
In correspondence with King’s College London, the regulator warned participants faced a “very likely” risk of fertility loss and permanent damage to bone health.
The MHRA also highlighted the “potentially significant and, as yet, unquantified risk of long-term biological harms” associated with the treatment and requested further discussions before the study could proceed.
On Friday, the regulator confirmed those concerns had been addressed following agreement on a modified protocol.
Researchers said the updated trial includes strengthened safeguards but stressed there had been “no major changes to the design or conduct” of the study.
King’s College London also said the MHRA’s concerns “were not based on the emergence of any new scientific evidence”.
The trial aims to recruit up to 250 children and young people receiving treatment through NHS gender services, making it the largest study of its kind in the UK.
Participants will receive puberty blockers for up to two years and will be closely monitored for potential side effects, including changes to bone density and vaginal bleeding.
Families will also receive enhanced information about fertility preservation, including egg and sperm freezing.
Puberty blockers, formally known as gonadotrophin-releasing hormone analogues, suppress the physical changes associated with puberty, including menstruation, breast development and facial hair growth.
The study cannot begin until an ongoing judicial review challenging the approvals granted by the MHRA and the Health Research Authority has concluded.
The NHS stopped routinely prescribing puberty blockers in 2024 following the Cass Review, which concluded there was insufficient evidence to support their use.
The report also warned they could place children on a pathway towards further medical intervention with cross-sex hormones.
Campaigners and cross-party politicians have previously called for the trial to be abandoned, arguing there is no ethical basis for conducting such research on children.
Helen Joyce, director of advocacy at Sex Matters, criticised the decision to restart the study.
“It is already clear that puberty blockers are no solution to childhood gender distress, and that they cause unacceptable harm,” she said.
She described the protocol changes as “trivial” and questioned whether children as young as 11 could meaningfully consent to the potential long-term risks.
