Dr Hilary Cass, the author of the landmark review on gender-affirming care for children in the UK, has defended the launch of a new puberty blocker trial. Cass says the research will ultimately prevent harm to young people by generating rigorous evidence on the safety and efficacy of these medications.
"I am absolutely convinced that more children will be harmed if we don't do the trial than if we do," Cass stated, addressing concerns from some advocacy groups who oppose further study of puberty blockers in minors. Her comments come as the NHS prepares to begin clinical trials examining the long-term effects of these drugs on bone health, growth, and psychological outcomes in children experiencing gender dysphoria.
The Cass Review, published in 2024, sparked significant debate across medicine, policy, and activism by recommending caution around gender-affirming treatments for under-18s. The review found limited evidence on puberty blockers' long-term safety profile and called for more robust research before widespread prescription to children. Cass emphasized that the trial represents the evidence-gathering approach her review advocated for, not a restriction on treatment.
Medical organizations including the Royal College of Paediatricians and Child Health have backed the trial design. Supporters argue that controlled research will either confirm puberty blockers' safety or identify previously unknown risks, allowing clinicians to make informed decisions. Without such data, they contend, prescribing happens in an evidence vacuum.
Critics worry the trials delay access to care that some young people view as lifesaving. Transgender youth advocacy groups have expressed concerns that framing puberty blockers as experimental could stigmatize young people already receiving them.
Cass framed the trial as the responsible path forward, balancing the urgent needs of individual patients against the requirement for population-level evidence. The research will ultimately inform policy and clinical guidance across the NHS and potentially influence international practice standards.