A clinical trial of drugs that can delay puberty can go ahead after a high court judge threw out a legal challenge on Friday.

Campaigners had launched the attempt to halt the planned research into puberty blockers, to be run by researchers at King’s College London (KCL), on the grounds that they believed it could harm the children taking part.

But Mr Justice Chamberlain refused the application for a judicial review; saying none of their claims had a realistic chance of success in court. He said each patient involved in the Pathways trial will have been assessed over “many months” by specialist doctors who will have “formed the opinion that a child has a reasonable prospect of receiving a clinical benefit from the treatment”.

The university welcomed the court’s decision on Friday, saying particular care would be taken over the safety of participants of the trial, which will start recruiting more than 220 children aged between 11 and 16 years old from 1 August.

But opponents, including the psychotherapist James Esses and Keira Bell, who began taking puberty blockers as a teenager before later detransitioning, expressed sadness at the ruling.

Bell told the BBC: “It’s a tragedy that the court has refused permission for this challenge to proceed. The medical profession and morality do not always walk hand in hand. If they did, this trial would be out of the question.”

The Bayswater Group, which was also part of the legal challenge, said: “We remain of the view that the Pathways trial does not meet the legal and ethical thresholds required for research on children.

“The design and scale of the study, the known and potential harms of the intervention, and the absence of a sufficient prior evidence base of benefit raise fundamental questions about whether the protective framework for minors has been properly implemented.”

A spokesperson for KCL said: “Pathways trial is a carefully designed study to give much needed evidence about the potential benefits and risks of puberty suppression to improve NHS care.

“A small number of young people with long-term gender incongruence, who have already received comprehensive psychological and social support through NHS gender services, will be eligible.”

The spokesperson added that the study will have “strict eligibility requirements” and that the trial’s design had been “carefully reviewed by independent researchers and has been approved by the UK’s health research regulators, the HRA and MHRA”.

The study was originally commissioned in response to a 2024 review of gender identity services by Dr Hilary Cass, which found that gender medicine was an “area of remarkably weak evidence” and “built on shaky foundations”. Initially used to treat early-onset puberty, puberty blockers had been prescribed off-label to children with gender dysphoria until the NHS banned their use last year after the Cass review.