Approximately 250 young people are expected to participate in the study which researchers anticipate will clarify whether suppressing puberty affects brain development
Hundreds of children are set to be jabbed with puberty blockers as part of an NHS-backed clinical study.
The controversial study will see as many as 226 children as young as ten-years-old who believe they are transgender take part. Children with gender dysphoria who take part may be allowed to continue using the medication after the study concludes, despite a UK-wide ban on prescribing them to under-18s with the condition, researchers have revealed.
Scientists have commenced a clinical trial investigating the effects of puberty blockers, with initial participants anticipated to begin enrolment in the new year. Researchers from King’s College London are optimistic that over 200 youngsters could ultimately participate in the study, with findings expected in approximately four years.
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Some participants may continue receiving the medication following the trial if it is considered “clinically appropriate”. The research team will additionally employ scans to examine whether the medication affects brain development as part of separate analysis launching on Saturday.
Both investigations are components of a broader Pathways research initiative, which is led by KCL, and is co-sponsored by King’s College London and the South London and Maudsley NHS Foundation Trust.
The Pathways research programme seeks to determine how the NHS can best support youngsters attending gender services.
Proposals for a puberty blockers trial were unveiled in 2024 after the publication of the Cass Review, which determined that the standard of research purporting to demonstrate the advantages of such medication for youngsters with gender dysphoria was “poor”.
The medication is no longer prescribed by the NHS to youngsters for treating gender dysphoria after a ban introduced in 2024 became permanent last December.
The trial has now commenced, with 226 young people anticipated to be enrolled. Researchers have been collaborating with clinical services to establish a pathway for patients involving psychological and social care, alongside obtaining 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 participants will typically be aged 10 to 11 for girls and 11 to 12 for boys, with a maximum age of consent at 15 years 11 months, researchers confirmed.
One cohort will receive puberty blockers for two years, whilst the other will be administered the medication after a one-year delay. Both cohorts will be monitored for two years and will know when they should anticipate receiving the treatment.
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 explained the rationale behind establishing a 12-month delay group was based on when researchers would realistically anticipate observing evidence of both benefits and potential risks and harms. She continued: “But of course we will be looking at whether young people and their parents change their minds.”
To participate in the trial, children must have begun puberty and received a diagnosis of gender incongruence, which occurs when they experience a mismatch between their gender identity and their biological sex at birth.
They must have experienced these feelings for more than two years, alongside a “persisting desire” to receive puberty blockers following psychological care. The parents or guardians of participants must also support the option of using puberty blockers.
Puberty blockers are typically administered as an injection, with the most common – called triptorelin – usually given every six months. The medications were initially approved during the 1980s for treating precocious puberty, which begins before age eight in girls and nine in boys.
The NHS states that girls typically begin puberty at 11, whilst boys start at 12.
Prof Simonoff noted the drugs demonstrate a “good safety profile” when used for delaying early puberty, however questions have emerged regarding their application in treating gender incongruence. These concerns encompass potential impacts on bone density, possible effects on reproductive capability and potential influences on neurological development.
The second research project being initiated is named Pathways Connect, which will examine the neurological development of young people taking puberty blockers compared with those who are not.
Researchers anticipate the study will clarify whether suppressing puberty affects brain development.
Approximately 250 young people are expected to participate – comprising roughly 150 from the puberty blocker clinical trial and 100 receiving non-medical gender care.
Prof Simonoff explained: “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.”
Other studies include Pathways Horizon, a longitudinal study of all young people attending NHS children and young people gender services who wish to participate. It will monitor the mental and physical health of youngsters under these services as they mature.
Meanwhile, Pathways Voices will incorporate the experiences of children and young people living with gender incongruence and their care within the NHS.
