Thousands of vulnerable children questioning their gender identity have been let down by the NHS providing unproven treatments and by the “toxicity” of the trans debate, a landmark report has found.

The UK’s only NHS gender identity development service used puberty blockers and cross-sex hormones, which masculinise or feminise people’s appearances, despite “remarkably weak evidence” that they improve the wellbeing of young people and concern they may harm health, Dr Hilary Cass said.

Cass, a leading consultant paediatrician, stressed that her findings were not intended to undermine the validity of trans identities or challenge people’s right to transition, but rather to improve the care of the fast-growing number of children and young people with gender-related distress.

But she said this care was made even more difficult to provide by the polarised public debate, and the way in which opposing sides had “pointed to research to justify a position, regardless of the quality of the studies”.

“There are few other areas of healthcare where professionals are so afraid to openly discuss their views, where people are vilified on social media, and where name-calling echoes the worst bullying behaviour. This must stop.”

NHS England commissioned her inquiry in 2020 amid rising concern over the care provided by the Tavistock and Portman NHS mental health trust’s gender identity development services (Gids). It treated about 9,000 children and young people, with an average age at referral of 14, during 2009-2020.

Her inquiry has already led to NHS England shutting Gids, banning puberty blockers and switching to a new “holistic” model of care in which under-18s experiencing confusion about their gender identity will routinely receive psychological support rather than medical intervention.

“For most young people, a medical pathway will not be the best way to manage their gender-related distress. For those young people for whom a medical pathway is clinically indicated, it is not enough to provide this without also addressing wider mental health and/or psychosocially challenging problems,” said Cass, an ex-president of the Royal College of Paediatrics and Child Health.

The report recommends that all such young people should be screened to detect neurodevelopmental conditions, such as autism spectrum disorder, and there should be an assessment of their mental health, because many who seek help with their gender identity also have ADHD, anxiety or depression, for example.

Some transgender adults “are leading positive and successful lives, and feeling empowered by having made the decision to transition”, Cass said. However, “I have spoken to people who have detransitioned, some of whom deeply regret their earlier decisions”, she added.

“While some young people may feel an urgency to transition, young adults looking at their younger selves would often advise slowing down,” the report says.

“Some of the young adults said to us they wished they’d known when they were younger that there were more ways of being trans than just a binary medical transition,” Cass told the Guardian.

In her report, she outlines how the Tavistock trust began prescribing puberty blockers much more widely in 2014, despite a lack of evidence that they helped.

In an interview with the Guardian, Cass said that gender-questioning children have been “let down” by the NHS, health professionals and a “woeful” lack of evidence about what treatment works.

“One of the things that has let them down is that the toxicity of the debate has been so great that people have become afraid to work in this area.

“A majority of people have been so afraid, because of the lack of guidance, lack of research, and how polarised this is that they’ve passed [patients] straight on to Gids.”

Wes Streeting, the shadow health secretary, said: “Today’s report must provide a watershed moment for the NHS’s gender identity services. Children’s healthcare should always be led by evidence and children’s welfare, free from culture wars. Clinicians and parents alike want the best for children at this crucial developmental stage. This report provides an evidence-led framework to deliver that.”

Sallie Baxendale, a professor of clinical neuropsychology at University College London, said that Cass’s report “has laid bare the worrying lack of evidence to support the treatments that were prescribed by NHS clinicians to children with gender distress for over a decade.

“These treatments inflicted significant harm on some of the most vulnerable children in our society.

“Exceptionalism often lies at the heart of medical scandals when services go rogue and start to operate outside the normal parameters of clinical practice.”

However, Dr Aidan Kelly, a clinical psychologist specialising in gender who left the Tavistock in 2021, said the NHS was struggling to recruit skilled and experienced people to run the planned eight clinics that will provide the new, broader model of care.

“Although Gids wasn’t perfect, we had a service with a history and expertise. There were things that needed to change but at least holding on to the knowledge that was accrued over time would have made sense to me,” he said.

Disputing many of Cass’s findings he said that a recent German review had found that puberty blockers were safe and effective. NHS England’s switch to a wholly different way of treating young people confused about their gender identity has left England “out of step with the rest of the world”, he added.

Cass disclosed in the report that six of the NHS’s seven specialist gender services in England for adults had “thwarted” an attempt by York University, at her request, to obtain and analyse the health outcomes of people who had been treated by Gids in order to improve future care.

This refusal to cooperate “was coordinated”, she told the Guardian. “It seemed to me to be ideologically-driven.”. Clinicians caring for those with gender-related distress are very divided on how best to do that, she acknowledges in the report.

It also documents how Gids experienced both an explosion in demand for its service from 2010, and also a huge increase in the number of birth-registered females, in a reversal of the pattern of referrals.

Cass said that “online influencers” had played a key role in fuelling confusion among young people about their gender identity and what they needed to do to change it.

“We haven’t done a comprehensive search but certainly when we were told about particular influencers I followed some of those up. Some of them give them very unbalanced information.

“And some of them [young people] were told that parents would not understand so that they had to actively separate from their parents or distance their parents. All the evidence shows that family support is really key to people’s well being. So there was really some dangerous influencing going on,” she said.

Rishi Sunak said: “We simply do not know the long-term impacts of medical treatment or social transitioning on them, and we should therefore exercise extreme caution.

“We acted swiftly on Dr Cass’s interim report to make changes in schools and our NHS, providing comprehensive guidance for schools and stopping the routine use of puberty blockers, and we will continue to ensure we take the right steps to protect young people.”