The letter from the Medicines and Healthcare products Regulatory Agency (MHRA) highlighted concerns including the \u201cvery likely\u201d loss of fertility and permanent bone damage to children. The drugs pause the physical changes of puberty, such as breasts, periods or facial hair.<\/p>\n
The MHRA said: \u201cWe would like to discuss the inclusion of a minimum age for participation in the trial \u2026 since potentially significant and, as yet, unquantified risk of long-term biological harms is present to participants and biological safety has not been definitively demonstrated in this proposed cohort, at the very least, there should be a graded \u2026 approach starting with those aged 14 as the lower limit of eligibility.\u201d<\/p>\n
It highlighted the infertility risk, stating: \u201cIt is widely understood that reduction in gametogenesis will very likely cause infertility in these young people. These are medically consequential effects for a future adult individual that may involve infertility treatment and significant medical interventions.\u201d<\/p>\n
Wes Streeting, the health secretary, had been facing pressure from dozens of MPs to halt the study. Streeting banned puberty blockers for under-18s in gender medicine in 2024 over fears they were harmful. They were given to children at the Tavistock clinic since 2011, but the NHS stopped using them in 2024 after the Cass review found there was little evidence to support their use.<\/p>\n
![\"Demonstrators](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/02\/\/278264e9-cdf4-403e-8f54-222f05efc6b1.jpg\")
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Protesters opposed to the use of puberty blockers campaigned outside the Department of Health and Social Care last year<\/p>\n
WIKTOR SZYMANOWICZ\/FUTURE PUBLISHING\/GETTY IMAGES<\/p>\n
In her final report Dr Hilary Cass warned of safety risks and recommended a trial into puberty blockers to fill an evidence gap about how best to treat gender dysphoria in children.<\/p>\n
The Department of Health and Social Care said: \u201cWe have always been clear about the red lines regarding this trial \u2014 ensuring the safety and well- being of the children and young people involved and always being led by the clinical evidence. The MHRA has now raised new concerns \u2014 directly related to the wellbeing of children and young people \u2014 and scientific dialogue will now follow with the trial sponsor.\u201d<\/p>\n
It said \u201cpreparations for the trial have been paused\u201d, adding: \u201c[It] will only be allowed to go ahead if the expert scientific and clinical evidence and advice conclude it is both safe and necessary.\u201d<\/p>\n
The MHRA said: \u201cIt is part of the usual process that clinical trials are kept \u2026 under review and for us to have active scientific dialogue with the trial sponsors. The safety and wellbeing of the participants to be recruited \u2026 is paramount, particularly in view of the age of the children [who] may be involved.\u201d<\/p>\n