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Claims by those speaking for the trans-lobby that puberty blockers are both safe and fully reversible are dangerously false. I am no medical expert, but the independent review commissioned by NHS England in 2020, led by Dr Hilary Cass, raises serious concerns about both the safety and reversibility of these puberty suppressing treatments.

The Cass Review debunks the myth that puberty blockers are safe and fully reversible. The final report highlights significant, long-term risks, and irreversible consequences.

The claim of safety is undermined by the lack of high-quality, long-term studies on the effects of puberty suppression on brain development, bone health, fertility, and psychosexual maturation. Research cited in the review shows that puberty blockers disrupt normal adolescent development, particularly executive function and decision-making abilities, and may permanently alter neurocognitive pathways (Cass Review, p. 175, Section 14.3). Additionally, bone density loss during puberty suppression has been observed, with uncertainty about whether full recovery occurs even after stopping treatment (Cass Review, p. 177, Section 14.8).

The claim that puberty blockers are fully reversible is also not supported by evidence. The Cass Review found that nearly all young people who start puberty blockers progress to cross-sex hormones, raising concerns that rather than offering a neutral "pause," these drugs reinforce medical transition (Cass Review, p. 178, Section 14.9). Furthermore, puberty blockers may permanently impact sexual development, as blocking testosterone or estrogen during puberty prevents the natural maturation of reproductive organs and sexual function, potentially leading to lifelong infertility and complications in later surgeries (Cass Review, p. 184, Section 15.2). Informed consent is another major issue, as many young people and their families are not fully aware of the irreversible consequences of these interventions when they begin treatment (Cass Review, p. 184, Section 15.3). The absence of strong clinical evidence, coupled with emerging data on permanent changes, directly contradicts the claim that puberty blockers are merely a harmless and reversible intervention.

Drilling into the Cass Review's final report uncovers some very serious concerns about puberty blockers and cross-sex hormones that warrant the immediate banning of these treatments for minors under 18. The following analysis of the final report might be helpful in your conversations with Members of Parliament, lawmakers, and parents, as they consider the suitability of these treatments.

1. Permanent Changes and Developmental Impact

  • Puberty blockers can cause permanent changes to adolescent development, particularly in sexual, gender identity, and neurocognitive formation. Adolescence is a critical period for neurocognitive development, sexual maturation, and social experience, and blocking puberty may have irreversible consequences (Cass Review, p. 175, Section 14.3).
  • Blocking sex hormones can lead to unintended long-term effects on brain development, sexuality, and gender identity formation, which are not yet fully understood (Cass Review, p. 175, Section 14.4).

2. Impact on Fertility and Sterility

  • Use of puberty blockers and cross-sex hormones can result in permanent sterility. The long-term impact on fertility remains uncertain, but some studies indicate that adolescents who undergo hormone treatments may lose reproductive capacity permanently (Cass Review, p. 184, Section 15.2).
  • Fertility preservation counseling is often inadequate, leaving many adolescents unaware of the risks before commencing medical transition (Cass Review, p. 184, Section 15.3).
  • Cross-sex hormones lead to profound endocrine changes, which may result in irreversible loss of fertility if initiated before gonadal maturation (Cass Review, p. 185, Section 15.4).

3. Effects on Neurocognitive and Physical Development

  • Puberty blockers negatively impact brain maturation, particularly in areas related to executive function, decision-making, and judgment. There is concern that prolonged use may permanently alter neurodevelopment (Cass Review, p. 175, Section 14.3).
  • Adolescents treated with puberty blockers for over a year exhibited worse executive functioning than those who did not receive them (Cass Review, p. 176, Section 14.5).
  • Use of puberty blockers in male patients may lead to insufficient genital growth, complicating later surgical options for those who transition (Cass Review, p. 176, Section 14.6).
  • Reduction in bone density has been observed in adolescents undergoing puberty suppression, which may not fully recover even after cessation (Cass Review, p. 177, Section 14.8).

4. Lack of Strong Evidence Supporting Reversibility

  • The claim that puberty blockers are fully reversible is not supported by strong evidence. The Cass Review states that no robust studies demonstrate that puberty blockers simply “pause” puberty without lasting effects (Cass Review, p. 176, Section 14.5).
  • A significant majority of those who begin puberty blockers proceed to cross-sex hormones, raising concerns that puberty blockers may not allow for true reconsideration but instead act as a pathway to irreversible transition (Cass Review, p. 178, Section 14.9).

5. Psychological and Psychosocial Effects

  • Despite claims that puberty blockers reduce distress, the evidence for psychological benefits is weak and inconsistent. Some studies report no improvement in gender dysphoria or mental health outcomes after their use (Cass Review, p. 179, Section 14.10).
  • There is no evidence that puberty blockers reduce suicide risk, despite common claims that they do (Cass Review, p. 179, Section 14.11).
  • Long-term psychosocial effects remain unknown, particularly in individuals who later detransition or experience regret (Cass Review, p. 180, Section 14.12).

6. Medical Concerns and Ethical Considerations

  • The review highlights that puberty blockers are used off-label, meaning they are not officially approved for treating gender dysphoria and lack high-quality long-term safety data (Cass Review, p. 176, Section 14.6).
  • Many young people and their families were not fully informed of the potential long-term consequences before starting treatment (Cass Review, p. 184, Section 15.3).
  • Concerns about medical ethics have been raised due to the lack of adequate informed consent processes, particularly given the long-term and potentially irreversible effects of these treatments (Cass Review, p. 186, Section 15.5).

Conclusion

The Cass Review raises serious concerns about the long-term effects of puberty blockers and cross-sex hormones on adolescents. The review finds insufficient evidence to conclude that these interventions are safe and reversible, and it warns of potential permanent sterility, neurodevelopmental changes, and other long-term consequences.

References with Page and Section Numbers

Cass, H. (2024). Independent Review of Gender Identity Services for Children and Young People. NHS England.

  • Permanent changes in adolescent development – p. 175, Section 14.3
  • Neurocognitive effects and executive function – p. 176, Section 14.5
  • Fertility and sterility concerns – p. 184, Section 15.2
  • Inadequate fertility preservation counseling – p. 184, Section 15.3
  • Irreversible loss of fertility due to cross-sex hormones – p. 185, Section 15.4
  • Bone density reduction and long-term effects – p. 177, Section 14.8
  • Reversibility of puberty blockers challenged – p. 176, Section 14.5
  • Locking adolescents into transition pathway – p. 178, Section 14.9
  • No evidence of suicide prevention benefits – p. 179, Section 14.11
  • Concerns about detransitioners and regret – p. 180, Section 14.12
  • Off-label use of puberty blockers and lack of safety data – p. 176, Section 14.6
  • Ethical concerns over informed consent – p. 186, Section 15.5