The UK has paused a clinical trial on puberty blockers after the medicines regulator raised safety concerns. The regulator warned about unknown long-term biological risks and set a minimum age of 14.
The Medicines and Healthcare products Regulatory Agency will meet King’s College London next week. They will review the study design and participant safety. The Department of Health and Social Care confirmed the recruitment delay.
The Pathways trial will not begin until experts resolve the concerns.
The study followed the Cass review, which found weak evidence for the drugs’ benefits in young people. Dr Hilary Cass said a controlled trial was the only way to clarify the effects.
The government said child safety remains the key condition. Clinicians are now examining the evidence. The trial will proceed only if it proves safe and necessary.
King’s College London said it will work closely with the regulator. It stressed that the project follows strict scientific standards and aims to guide future treatment decisions.
Researchers had planned to recruit 226 participants over three years. The original design allowed children as young as ten. The regulator now demands a stepwise approach that starts at 14 because long-term risks remain unclear.
NHS England already limits puberty blockers to research settings. The Cass review had advised ending routine use.
Professor Sir Jonathan Montgomery said the pause strengthens the protocol rather than stops the trial. He called the move a proper safety measure.
