Puberty Blockers Trial Paused in UK Amid Safety Concerns

A clinical trial assessing the utilize of puberty blockers in children questioning their gender identity has been paused following new concerns raised by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA). The pause impacts the Pathways trial, which aimed to gather evidence on the risks and benefits of these medications for young people experiencing gender incongruence.

MHRA Raises Concerns, Trial Paused for Review

The MHRA has expressed concerns regarding the age limit for participants and the require for more detailed monitoring of potential long-term effects. Discussions between the MHRA and King’s College London, the trial sponsor, are scheduled to start next week to address these issues. Recruitment for the trial will remain suspended until the concerns are resolved [1].

A Department of Health and Social Care spokesperson emphasized that the safety and wellbeing of children and young people are paramount. “The MHRA has now raised new concerns – directly related to the wellbeing of children and young people – and scientific dialogue will now follow with the trial sponsor,” they stated [1].

Background: The Pathways Trial and Cass Review

The Pathways trial was initiated following recommendations from the Cass review, an independent review of gender identity services for children and young people in England. The Cass review highlighted a weak evidence base for the benefits of puberty blockers and suggested a trial was necessary to gather more robust data [3].

Puberty blockers, likewise known as puberty suppressing hormones (PSH), are used to delay the physical changes of puberty. In 2024, their routine use for under-18s questioning their gender identity was banned, with access limited to research settings [2].

Specific MHRA Concerns

The MHRA has specifically suggested raising the minimum age for trial participants from 10 to 14. The agency also called for more rigorous monitoring of bone density and a more detailed consent process [2]. The MHRA expressed concern over the “unquantified risk of long-term biological harms” to younger participants [3].

King’s College London Response

King’s College London affirmed its commitment to the wellbeing of young people with gender incongruence and their families. A spokesperson stated the institution will continue to collaborate with the MHRA to address their concerns, emphasizing the scientific rigor of the trial’s design [1].

The trial had initially planned to recruit over 220 children aged 11 to 15 over a three-year period [2].

Regulatory Process Working as Intended

Experts have noted that the pause demonstrates the regulatory process functioning effectively to prioritize participant safety. Professor Sir Jonathan Montgomery of University College London stated that the discussions are focused on strengthening the trial protocol and are not the result of legal challenges [2].