Systematic reviews in gender care

The University of York conducted several systematic reviews commissioned by the Cass Review on puberty blockers, cross-sex hormones, social transition, and treatment outcomes in young people with gender dysphoria.

York reviews for the Cass Review

The University of York conducted several systematic reviews commissioned by the Cass Review on puberty blockers, cross-sex hormones, social transition, and treatment outcomes in young people with gender dysphoria. The reviews were published in 2024 in BMJ Archives of Disease in Childhood.

NICE reviews (2020)

In 2020, the UK’s NICE published two evidence reviews concluding that the evidence for the effects of puberty blockers and cross-sex hormones on psychological well-being in young people was of very low quality. A summary of both reviews is available on transkompas.nl.

SBU (Sweden) and COHERE (Finland)

Swedish and Finnish health technology assessment bodies reached similar conclusions. These reviews provide the scientific basis for the policy changes in Scandinavia.

What the York reviews found

The review of puberty blockers included fifty studies, only one of which was of high quality. The review of hormones in young people included 53 studies, again with only one considered high quality. The researchers concluded that, based on this material, it is not possible to make a reliable statement about the effects on gender dysphoria or on psychological and psychosocial health. The same applied to social transition and psychosocial interventions. A separate review assessed international guidelines and found that most were methodologically weak; see the Endocrine Society guideline.

Later reviews

Reviews have also been published outside the United Kingdom. In 2023, Swedish researchers published an updated systematic review in Acta Paediatrica, reaching the same conclusion about the weakness of the evidence. A group led by Canadian methodologist Gordon Guyatt, one of the founders of evidence-based medicine, published reviews on blockers and hormones in 2025 and rated the certainty of the evidence as very low. Researchers who examined thirty years of research on the Dutch Protocol concluded that reliable evidence is lacking. In 2025, the US Department of Health and Human Services published an overview of the existing reviews; see the timeline.

Why reviews carry more weight than individual studies

A systematic review uses a predefined method to identify all studies addressing a particular question and assesses the quality of each study. This prevents only favorable results from being cited. The fact that independent teams in different countries reached the same conclusion gives that conclusion weight. The reviews do not say that the treatment does not work. They say that this is not known. See also the evidence pyramid.

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