Dr. Hilary Cass, the author of the major independent review of gender-affirming care for children in England, has thrown her support behind a planned trial of puberty blockers. The trial aims to generate robust evidence about the safety and efficacy of these medications in young people questioning their gender identity.
Cass expressed confidence that conducting the research will ultimately protect children from harm. "I am absolutely convinced that more children will be harmed if we don't do the trial than if we do," she stated, underscoring her position that evidence gaps about puberty blockers create their own risks.
Her 2024 Cass Review examined gender-affirming medical practices for minors and concluded that the evidence base for many treatments, including puberty blockers, remains incomplete. The review recommended that any continued prescribing of these medications occur within formal research settings where effects can be carefully monitored and studied.
Puberty blockers, primarily gonadotropin-releasing hormone agonists, temporarily pause puberty development. They give young people time to explore their gender identity without permanent physical changes. However, questions persist about their long-term effects on bone health, fertility, and psychological outcomes.
The proposed trial represents a middle path between continuing widespread prescribing without systematic data collection and restricting access entirely. By enrolling young people in a structured study, researchers can document outcomes systematically while still providing treatment access to those who need it.
Cass's endorsement carries weight in clinical circles. Her review prompted major changes to gender-affirming care protocols in the NHS, including increased psychological assessment before medical interventions and restrictions on puberty blocker use to research settings.
This approach reflects a broader shift toward what Cass calls "cautious optimism grounded in evidence." Rather than ideology driving policy, the emphasis moves toward letting robust research inform clinical decisions. The trial will help answer longstanding