A top Oxford University scholar has added his voice to a growing list of experts who warn against puberty blockers for transgender children, saying they may be harmful and irreversible long term.

Professor Ashley Grossman, an endocrinologist, says there's 'no good evidence' showing puberty blockers help trans children, highlighting a new study which found they damage the testes and sperm of the boys who take them.

That study, and Professor Grossman's comments, bring into question the 'reversibility' of puberty blockers — a key claim of the trans campaigners who promote the drugs and say they 'pause' puberty and buy time for trans kids to make decisions about their gender.

Grossman's comments come ahead of the release of the long-awaited Cass Review in the UK, which is set to confirm a shift away from the medicalized treatment of trans children to one based on support and talk therapy.

Prof Ashley Grossman, a University of Oxford endocrinologist, says there's 'no good evidence' showing puberty blockers help trans children

Trans activists say puberty blockers and other gender-affirming care is life-saving among a suicide-prone group 

'Studies have shown that there is no good evidence for the routine use of puberty blockers,' Grossman said in a statement.

'Indeed, there are some recent early data — although not yet peer-reviewed or published — suggesting some of their effects on testes and sperm may not be reversible.'

Grossman said blockers may be 'helpful' to some trans kids, but that the drugs were too risky to be dolled out to the 'greatly increased' number of young people who identify as trans nowadays.

'Routine puberty blocking treatment for this use has not yet been adequately studied, and many of these children may have other problems for which they need help,' he added, hinting at a growing body of evidence showing gender confused youngsters often have other, underlying mental health issues.

His comments take aim at one of the most controversial issues of our time — whether to provide drugs and surgery to kids who experience gender confusion or 'dysphoria' and ask their parents or doctors for help.

Puberty blockers were originally developed to suppress the hormones of minors who started puberty too early.

They are nowadays prescribed off-label to a fast-growing number of trans children.

Advocates of gender-affirming care, as it is known, say it's life-saving for a suicide-prone group, and that puberty blockers help pre-teens 'pause' their puberty and buy time to weigh life-altering decisions.

Puberty blocker prescriptions continue to rise in the United States

Most children who get treated with puberty blockers go on to cross-sex hormones, like this patient at Blue Mountain Clinic in Montana

Critics warn of surging numbers of young people who identify as trans, and say puberty blockers, cross-sex hormones and surgeries are often unnecessary and likely dangerous.

Children will NOT be prescribed puberty-blockers

Ministers hailed the landmark ruling, arguing it would help ensure care is based on evidence and is in the 'best interests of the child'. 

Republican lawmakers have outlawed puberty blockers and other types of trans care for minors in nearly two dozen states.

Norway, Finland, Sweden, Holland, and the UK are among a growing list of European countries to have restricted or wholesale stopped trans interventions on children.

Britain is readying for the long-awaited release of a review by the leading consultant pediatrician Hilary Cass will shape NHS England's future care for trans children and young people, due o Wednesday.

Early reports suggest it will warn of the lack of data about the safety of trans hormones for children, and propose a more holistic care package that assesses whether young patients suffer from mental health issues other than gender anxiety.

This puts Britain at odds with the influential American Academy of Pediatrics (AAP), which recently suggested that it is child abuse to deny gender-affirming care to minors.

America's leading pediatric group said that ‘withholding [gender-affirming care] is harmful to children and amounts to state-sanctioned medical neglect and emotional abuse.’

The AAP made the claim in a consensus statement published in late December and the declaration was in response to a wave of age restrictions on puberty-blocking drugs and surgeries for children in Republican states.

While its views are not medically binding, the panel is made up of 70,000 of the country's top child doctors and its recommendations are considered the gold-standard.

Chloe Col, 19, who transitioned to male at 13 before later regretting her decision at 16, is among a growing number of young people who come to regret their trans treatments and seek to reverse them. She says she regrets taking puberty blockers at the age of 13 years

Puberty blockers are prescribed off-label to a fast-growing number of trans children

Transgender campaigners responded angrily to the direction of the Cass Review.

They argue that trans children are stigmatization and face abuse, and that many will take their own lives unless doctors give them the hormones and surgeries that affirm the sex they identify with.

'Trans children face harm and injustice at every turn,' the account TransSafetyNow posted on X/Twitter.

'The Cass Review's final report does nothing to help trans children live happy, healthy, safe and confident childhoods.'

A Mayo Clinic study released this month found that puberty blockers can lead to withering testicles, fertility problems and even cancer among the trans kids who take them, in the latest study to raise alarm about transgender medicine.

They found that puberty blockers hurt the development of testicles and sperm production in ways that are not fully reversible and could affect users' ability to have children when they grow up.

The Mayo Clinic's 33-page study revealed puberty blocker damage at the cellular level 

'At the tissue level, we report mild-to-severe sex gland atrophy in puberty blocker-treated children,' the geneticist Nagarajan Kannan and others wrote in the 33-page study.

'We provide unprecedented histological evidence revealing detrimental pediatric testicular sex gland responses' to the drugs.

Researchers highlighted the case of a 12-year-old boy who had taken puberty blockers for 14 months.

Nearly 60 percent of his sex glands had 'fully atrophied,' they said.

There was also an 'appearance of microlithiasis,' or small clusters of calcium that are linked to testicular cancer.

In a 14-year-old patient who had been on puberty blockers for four years, they found his sperm production cells were stunted.

Scientists at the world-famous clinic said the results were worrying, but that more research was needed.

The evidence of sex 'gland atrophy and abnormalities from the histology data raise a potential concern regarding the complete 'reversibility' and reproductive fitness' of sperm cells in boys who take puberty blockers, it said.

The study came on the heels of the so-called 'WPATH files' — leaked messages from the world's top body for gender-affirming care, which showed clinicians behaving more like activists keeping quiet about the massive downsides of trans medicine.