BREAKING: NHS-backed puberty blocker trial PAUSED as regulator raises safety concerns. The Medicines & Healthcare products Regulatory Agency (MHRA) has requested the King’s College trial team amend study protocol, to better reflect risks to children https://assets.publishing.service.gov.uk/media/6998b06d047739fe61889efb/Sponsor-letter110226.pdf…

Trial team are asked to increase the minimum age of participants to 14 because of fertility concerns.

MHRA explicitly recognises "sterilising effect of puberty blockers followed by cross sex hormones and that gamete retrieval to preserve fertility is not possible at the stage when puberty blockers are given (Tanner stage 2) as neither sperm nor ova have matured."

Neither the protocol nor patient information sheets currently do this, as I have written about here: https://www.newstatesman.com/politics/2025/12/will-the-new-puberty-blocker-trial-put-children-at-risk…

And the lack of adequate explanation on fertility risk in Patient information sheets here: https://www.newstatesman.com/investigation/2026/01/nhs-puberty-blocker-trial-information-ignores-or-minimises-critically-important-risks…

The MHRA rightly points out, I do in the long-read above, that - as currently designed - the youngest participants could face being on blocker for years, or "many years of therapy to bridge" between ending two-year trial period and moving onto hormones (at 16 years old)

MHRA expresses concern about the use of KIDSCREEN 10 questionnaire as the principle outcome measure: "the physiological and pharmacological impacts may long outlast and outweigh any Quality of Life detected differences." (Here's what I wrote in December...)

MHRA is worried about the impact of blocking puberty in adolescence on bones too. "available data suggest treatment with triptorelin (drug used in the trial) beyond 12 months will result in persistent and potentially permanent bone structural change." As a result...

MHRA wants to discuss with trial team changing criteria so that children will be withdrawn if problems with bones identified after 12 months, inc: - clinically sig decline in bone mass density - any vertebral fracture - emerging failure to grow (height)

MHRA also suggests amending protocol to inc. a) withdrawal of any female from the trial who experiences more than two weeks of vaginal bleeding b) "adverse functional MRI changes detected at any time" - showing cognitive impairment from the blockers

Gov says safety & wellbeing of children has always been a "red line" & it will be "led by the clinical evidence...As the evidence is now being interrogated by clinicians, preparations for the trial have been paused while the MHRA and clinical leaders work through these concerns"

Full Department of Health and Social Care statement here: https://www.gov.uk/government/news/pathways-clinical-trial-paused-following-new-mhra-advice…

All of the issues raised above by the MHRA have been voiced by concerned clinicians and by those of us who have followed this area of medicine for several years. They're all contained in my original analysis from December, as an example. (ENDS) https://www.newstatesman.com/politics/2025/12/will-the-new-puberty-blocker-trial-put-children-at-risk…