Stop the Puberty Blockers Trial

We don't need to suppress the puberty of more children to prove that it's a very bad idea.

Claire Loneragan

Dec 16, 2025

If you have written to your MP recently objecting to the proposed puberty blockers trial you may well have had a response similar to the one I received.

The gist of it is that whilst he “absolutely agree[s] that the safety and wellbeing of children must always come first” and that “care for children experiencing gender distress must be rooted in evidence and must prioritise safeguarding, talking therapies, and support for both the child and their family”, this trial is needed “to establish evidence where it is currently lacking and to ensure that exceptional cases, where clinicians believe puberty blockers may be appropriate, can be assessed under strict, transparent, and independently monitored conditions. A moratorium without scientific assessment would leave clinicians, families, and young people in even more uncertainty.”

(As if the future health and well-being of more than 200 children is a price worth paying in order to eliminate uncertainty.)

I don’t suppose I will convince him, but since Hannah Barnes made such a compelling case against the trial in her recent article for The New Statesman I thought it was worth sharing eight of the reasons she gave. My MP is unlikely to read Hannah’s excellent article, but he is supposed to read letters from constituents. Maybe a few seeds of doubt will be sown.

1. There is no control group

All participants will be given puberty blockers - there is no group who are to be given a placebo - because it would be obvious which group that was. Therefore, the trial will, at best, be able to report on the difference in giving puberty blockers immediately versus waiting for one year.

However, all the children in the group given puberty blockers immediately will be predisposed to be happier in the short term (because they are getting what they want which is puberty blockers now) compared to those who wait.

Because outcomes will be judged by how happy the children are, this is a trial which will almost certainly report that giving children what they want immediately makes them happy. In the short term.

2. The time frame is far too short

The timeframe for reviewing results is just two years, but it is impossible to understand whether choices that impact a person for their whole lifetime were the right ones in such a short timeframe and when they are still a child. And ALL the participants will still be children after two years since they will all be under 16 years old when the trial commences. For a child who is 10 when the trial commences (as is proposed) he or she won’t even be a teenager when the follow up period ends.

3. Puberty blockers are not a standalone intervention

Systematic evidence reviews have shown that in the UK, 98% of children who were given puberty blockers progressed to cross sex hormones. This points to puberty blockers locking a child into their transgender ideation rather than giving them “time to think”. Despite this, they are being tested as if a standalone treatment, and the trial is characterised as a trial of puberty blockers only although the evidence suggests that approximately 220 of the 226 children involved will go on to cross sex hormones.

(There is no suggestion that these children will be denied cross sex hormones when they reach 18 years of age - indeed it’s hard to see how that could be ethically justified in the context of having already halted their puberty).

4. Girls are likely to be disproportionately affected for no good reason

Three further reasons for puberty suppression are considered:

• reducing or preventing worsening of distress;

• improving mental health;

• stopping potentially irreversible pubertal changes which might later make it difficult for the young person to “pass” in their intended gender role.

There is no evidence for the first or second claims.

The third claim is proven for boys. But because testosterone is such a powerful drug, it successfully masculinises women who have been through natural puberty, so we know that girls do not need their puberty suppressed to “pass”. Indeed, they may pass more successfully if they do not have their puberty blocked since they are likely to be taller. We also know there are significantly more teenaged girls identifying as “transgender” than boys, so it is likely that the trial children will comprise more girls than boys despite the potential benefits for them being practically non-existent.

5. There is no clear statement of the potential benefits of puberty blockers

We should not be giving children irreversible medical interventions without being able to say why. The Labour government summarised Cass’s final review as concluding that “the rationale for early puberty suppression remains unclear”.

What other area of medical research would permit a clinical trial on children without being able to explain what benefit they might derive?

6. There are no objective criteria to identify which children are likely to benefit

The children selected for the trial must have a diagnosis of “gender incongruence”.

This is defined by the WHO’s diagnostic manual as “a marked and persistent [at least two years] incongruence between an individual’s experienced gender and the assigned sex, which often leads to a desire to ‘transition’, in order to live and be accepted as a person of the experienced gender”.

A definition that only makes sense if sex is “assigned” (it isn’t) and “experienced gender” is an objective reality that can be somehow measured. But it is such a contested idea that there is little agreement on what is even meant by “experienced gender”.

Clinicians must also believe that there is “a reasonable prospect of benefit” for each child, but there is nothing on which to base this belief.

There was a small trial between June 2011 and April 2015 that included a group of 44 “highly selected” children. In other words, children who would be most likely to benefit because they had longstanding distress around their sex. That trial showed the drugs provided no clinical benefit: “no changes in psychological function, quality of life or degree of gender dysphoria.”

A later re-analysis of the study data showed outcomes for individual children varied widely:

• Approx one third saw their mental health deteriorate significantly,

• Approx one third saw no change

• Approx one third saw significant improvement.

Long term outcomes are not available, but in two thirds of cases the children were not helped. No criteria were established that would help clinicians to determine which cohort any child would fall into.

7. Puberty blockers lead to infertility, anorgasmia, and other health issues

Although we don’t know which children could fall into that third group of improved mental health, we do know that the intervention of puberty suppression if given early enough combined with progression to cross sex hormones (and almost all do) will result in irreparable damage.

The sperm and eggs of children whose puberty is blocked effectively will not have the opportunity to mature leaving them infertile as adults. They will never experience orgasm and there are known risks to bone density, memory and cognitive ability.

8. We already have data from approximately 2,000 children

Around 9,000 children passed through the GIDS clinic at the Tavistock. Of those, it is estimated that around 2,000 were given puberty blockers - the exact number is unknown, which is a cause for concern in its own right.

The Cass Review  requested the outcomes data for both those who been referred for medical treatments and those who had not, many of whom had been later referred to adult gender services as they turned 17 or 18 years old. The NHS adult gender services refused to cooperate with data sharing​ –​​ t​​​hey blocked the study.

Until that extant data is analysed, it is unconscionable that we would run an experiment on healthy children with no clear understanding of benefits, but with known serious risks.

In the interests of maintaining the highest standards of safeguarding, transparency, and evidence-based care, any MP supporting the trial should be comfortable that these points have been satisfactorily addressed. And if not, they must surely demand that the trial is paused until answers are found.

Children and young people deserve nothing less.

Do feel free to copy any or all of the above if you would like to share it with your MP.