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Criticism of the Dutch Protocol (VUmc/Cohen-Kettenis)

The Dutch Protocol — developed by Peggy Cohen-Kettenis and colleagues, first in Utrecht and later at VUmc in Amsterdam — became the international model for puberty suppression in young people with gender dysphoria. The best-known study followed 70 adolescents without a control group (source). The Cass Review calls care for these young people "an area of remarkably weak evidence" (source).

What the protocol involved

In the original protocol puberty suppression started from age 12 in early puberty, followed by cross-sex hormones from around age 16 and surgery from 18 (source). It was intended for a specific group: young people with gender dysphoria since childhood, without serious psychological problems and with family support.

The core studies

The evidence for the protocol came mainly from two publications on the same cohort: de Vries et al. (2011) describe the first 70 adolescents who received puberty suppression between 2000 and 2008, compared before and after treatment (source), and de Vries et al. (2014) followed them until after surgery; the final measurement included 55 of the 70 (source). WPATH SOC 7 and SOC 8 also built on this basis. See also the paediatric rollout from 2000.

Problem 1: no control group

No group without medical treatment was compared. Without a control group it cannot be established whether improvements are due to the treatment or to other factors, such as psychological support or natural development. The systematic review for the Cass Review rated the studies on puberty blockers mostly as moderate or low quality (source).

Problem 2: a death after vaginoplasty

One participant died after a vaginoplasty from necrotising fasciitis; the study by de Vries et al. (2014) reports this (source). The death is thus described in the publication itself.

Problem 3: attrition and selection

According to the Cass Review, the 70 were a subset of 111 consecutive referrals, selected because they were the first ready for the next stage of treatment (source). In the original study 89% of the patients were same-sex attracted to their birth-registered sex (source). The protocol was developed for a different group than the young people who started presenting from 2014 (see ROGD and the shift after 2010) (source).

Problem 4: the outcome measures

Michael Biggs (2023) reviews the origins and evidence of the Dutch Protocol and concludes that the claims used to justify puberty suppression, namely that it is reversible and aids diagnosis, have become less and less plausible. According to the Cass Review, outcomes such as bone health, fertility and sexual function have been insufficiently studied (source).

Problem 5: other countries

The UK's GIDS started an "early intervention study" in 2011 with inclusion criteria following the Dutch Protocol; Carmichael et al. (2021) found no change in psychological function in 44 young people (source). Karolinska in Stockholm decided in spring 2021 to start hormonal treatment of minors only within research, citing a 2019 SBU knowledge overview and the British Bell case (see SBU Sweden). NHS England closed GIDS in 2024 (see closure of Tavistock GIDS) and no longer provides puberty blockers routinely (source).

What this means

The Dutch Protocol, the basis of international policy, rests on one cohort of 70 adolescents without a control group, selected from a group that differs from the young people presenting today. In the Netherlands, the Health Council judged on 30 June 2026 that care is carefully organised, while rating the strength of the evidence for the effects found as low to very low (source). See also the Dutch rollout and the WPATH Files.