Plans for a puberty blockers trial were announced in 2024 following the publication of the Cass Review.
Some children with gender dysphoria recruited to a trial on puberty blockers could remain on the drugs after the study ends despite them being banned in the UK to treat under-18s with the condition, researchers have said.
Experts have launched a clinical trial looking at the impact of puberty blockers, with the first patients expected to be available for recruitment in the new year.
Researchers from King’s College London are hopeful that more than 200 children could eventually join the study, with results expected in around four years. Some could remain on the drugs beyond the trial if deemed “clinically appropriate”.
The team will also use scans to assess if the drugs impact brain development as part of separate analysis being launched on Saturday.
Both studies form part of a wider Pathways research programme, which is aiming to find out how the NHS can support children attending gender services.
Plans for a puberty blockers trial were announced in 2024 following the publication of the Cass Review, which concluded that the quality of research claiming to show the benefits of such medication for youngsters with gender dysphoria was “poor”.
The drugs are not prescribed on the NHS to children for the treatment of gender dysphoria after a ban in 2024 was made permanent last December.
The trial has now been launched, with 226 young people expected to be recruited.
Researchers have been working with clinical services to develop a process for patients to go through psychological and social care, as well as giving informed consent.
Chief investigator Emily Simonoff, professor of child and adolescent psychiatry at KCL’s Institute of Psychiatry, Psychology and Neuroscience (IoPPN), said: “We are expecting that the first group of young people who have gone through all of that, and have been reviewed by the national multidisciplinary team and ratified as clinically eligible, will be available for recruitment early in the new year.”
The youngest patients will typically be 10 to 11 for girls and 11 to 12 for boys, with a maximum age of consent at 15 years 11 months, researchers said.
One group will be given puberty blockers for two years, while the other will be given the drugs after a one-year delay.
Both groups will be followed up for two years and will be aware of when they should expect to be given the medication.
Prof Simonoff said: “At the end of two years, half of the young people, approximately, will have had one year of puberty suppressant hormones. Half of them will have had two years of puberty suppressive hormones.
“That also allows us to explore additional interesting questions, such as does the amount of time on receiving puberty suppression lead to increased effects, if they exist.
“At the end of the trial, each young person will be reviewed individually and clinically to look at their ongoing care needs, which may include remaining on puberty suppressing hormones, if that’s deemed clinically appropriate for them.”
Prof Simonoff said the thinking around creating a 12-month delay group was down to when researchers would realistically expect to see evidence both of benefits and possible risks and harms.
She added: “But of course we will be looking at whether young people and their parents change their minds.”
To take part in the trial, children must have entered puberty and must have a diagnosis of gender incongruence, which is when they feel a mismatch between their gender and their sex at birth.
They must have had these feelings for more than two years, as well as a “persisting desire” to take puberty blockers following psychological care.
The parents or guardians of patients must also support the option of using puberty blockers.
Researchers expect to see around five to six children a month recruited.
“That’s based on the number of young people that we expect to be seen each month in the different services,” Prof Simonoff said.
Findings from the trial will take “at least” four years, according to researchers.
Puberty blockers are typically given as an injection, with the most common – called triptorelin – usually administered every six months.
The drugs were first licensed in the 1980s to treat early puberty, which occurs before the age of eight in girls and nine in boys.
According to the NHS, the average age for girls to start puberty is 11 while for boys it is 12.
Prof Simonoff said the drugs have a “good safety profile” when used to delay early puberty, but concerns have been raised about their use to treat gender incongruence.
This includes potential impact on bone health, possible effects on fertility and possible effects on brain development.
The second study being launched is called Pathways Connect, and will look at the brain development of youngsters taking puberty blockers and those who are not.
It is hoped the research will shed light on if suppressing puberty impacts the development of the brain.
About 250 young people are expected to take part – including around 150 from the clinical trial of puberty blockers and 100 who are accessing non-medical gender care.
Prof Simonoff said: “We know that adolescence is a time of rapid brain development and rapid accrual of new thinking abilities, and people have raised the theoretical risk that interfering with puberty during this important time might impact brain development and cognition.
“There have been remarkably few studies in this area.
“We will be matching the brain-imaging findings to findings on everyday cognitive tasks and tests that they perform in clinic every day, so that we will understand what’s the relationship between any changes in brain development.”
The Pathways research programme is being led by KCL, and is co-sponsored by King’s College London and the South London and Maudsley NHS Foundation Trust.
Other studies include Pathways Horizon, a longitudinal study of all young people attending NHS children and young people gender services who wish to take part.
It will track the mental and physical health of youngsters under these services as they grow.
Meanwhile, Pathways Voices will include the experiences of children and young people living with gender incongruence and their care within the NHS.
