The UK has stopped a planned clinical trial on puberty blockers for children after the medicines regulator raised safety concerns. The regulator warned about unknown long-term biological risks and called for a minimum age of 14.
The Medicines and Healthcare products Regulatory Agency will hold talks with King’s College London next week. The Department of Health and Social Care confirmed that the Pathways trial will not recruit participants until they resolve the issues.
The study followed a recommendation from the Cass review into gender care for young people. The review found weak evidence for the benefits of puberty blockers. Dr Hilary Cass said a trial offered the only way to produce clear answers.
The government said safety and clinical evidence will guide every decision. Experts will now examine the data while preparations remain paused. The trial will proceed only if specialists confirm that it is safe and necessary.
King’s College London said it will continue to work with the regulator. The university stressed that the project uses strict scientific methods and aims to support informed future choices.
Researchers had planned to recruit 226 young people over three years. The original design allowed participants as young as ten, but screening would likely raise the average age.
The regulator has now asked for a step-by-step approach that begins at 14. It cited uncertain biological risks and suggested later studies could include younger groups.
NHS England had already restricted puberty blockers to research settings after the Cass review. Professor Sir Jonathan Montgomery said the pause shows the safety system working and aims to improve the study, not cancel it.
