The UK has paused a clinical trial on puberty blockers for children after the medicines regulator intervened. The regulator warned about unquantified long-term biological risks. It demanded a minimum participant age of 14.
The Medicines and Healthcare products Regulatory Agency will meet the sponsor, King’s College London, next week. They will address concerns about participant wellbeing. The Department of Health and Social Care confirmed the delay on Friday.
The Pathways trial will not recruit participants until they resolve the issues.
The Cass review recommended the study. The review found poor evidence for claimed benefits of puberty blockers in young people. Dr Hilary Cass said the evidence base was very weak. She argued that only a clinical trial could clarify the treatment’s effects.
A Department of Health and Social Care spokesperson stressed strict safety limits. The spokesperson said clinicians will examine the new evidence. Preparations will remain paused during this process. The trial will proceed only if experts confirm safety and necessity.
King’s College London said young people’s health remains its priority. The university will continue working with the regulator. It described the trial as scientifically rigorous. It said the research aims to support better future decisions.
Researchers had planned to recruit 226 participants over three years. The original design allowed children as young as ten. The team expected most participants to be older after screening.
The regulator has now challenged that age range. It requested a stepwise approach that starts at age 14. It cited uncertain long-term biological risks. It suggested later studies might include younger children.
The paused project is one of two planned studies on puberty blockers. The 2024 Cass review had recommended banning routine use. NHS England then restricted the drugs to research settings.
Professor Sir Jonathan Montgomery said the regulator wants to strengthen the protocol. He said the action does not aim to cancel the trial. He stressed that safety drives the process. He called the pause a sign that regulation works properly.
