Puberty blocker trial will help reduce harm, says Cass report author

A trial examining the risks or benefits of drugs that can delay puberty for gender-questioning children will help reduce harm, according to the author of a landmark review.

Dr Hilary Cass said she was "absolutely convinced that more children will be harmed if we don't do the trial than if we do."

Her comments follow pressure from campaigners and some politicians to have the research programme scrapped after it was announced children as young as 11 could be recruited onto the trial.

The Pathways clinical trial will be run by researchers at Kings College, London (KCL). In addition to setting a minimum age, they have also increased the safeguards for participants.

The puberty blockers research was recommended by Dr Cass after her 2024 review of gender medicine for children pointed to weak evidence behind their use.

Speaking to the BBC, Dr Cass said she believes since then "some of the hype about risks have been exaggerated in that we genuinely don't know if there are harms."

And she said the trial was "essential" to answer the question about "whether these drugs are helpful or not".

She added that young people will be "closely monitored in every respect" and the drugs stopped if concerns emerge.

The researchers will examine the impact of the drugs on the physical, social and emotional wellbeing of participants. This will include checks on bone density, brain function and fertility.

Cass believes without a trial young people will continue to get drugs from "unregulated and dangerous routes."

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Source: BBC News, 22 June 2026