Studies › Replication · Last reviewed 2026-05-16
Replication attempts
Summary
Attempts to replicate the positive outcomes of de Vries 2014 outside the Netherlands have produced mixed results. The Tavistock GIDS "Early Intervention Study" (Carmichael 2021) reported no statistically significant psychological improvement on GnRHa. Costa et al. (2015) reported limited effects. The Cass Review (2024) concluded that the positive Dutch outcomes have not been independently replicated.
1. Costa et al. 2015 (UK / Italy)
A longitudinal study of 201 youth in the Tavistock GIDS clinic, of which a subgroup received GnRHa. Both groups — with/without GnRHa — showed comparable improvements on the Children's Global Assessment Scale (CGAS) over 18 months. Adding GnRHa was not associated with additional improvement beyond psychological support.1
2. Carmichael et al. 2021 — Early Intervention Study
English study (n=44) of adolescents on GnRHa in the Tavistock GIDS, published after delay in PLOS ONE. The authors found "no statistically significant changes in psychological functioning … in this group as a whole" over ~36 months follow-up.2
3. Italian cohort (Costa 2016)
A smaller Italian cohort study reported improvements on psychological outcome measures after GnRHa, but the authors acknowledge a limited sample size and absence of a control group.3
4. Cass Review conclusion
"The systematic review by the University of York found that the studies conducted following the original Dutch cohort did not demonstrate the same positive outcomes for gender dysphoria, mental health or wellbeing."
— Cass Review, April 2024, p. 178
See also
- Original cohort: de Vries 2014
- Clinical context (UK): Tavistock GIDS
- Systematic evaluation: Cass Review 2024, SBU 2022
- Methodological analysis: Methodological criticism, Biggs
- People register — Costa, Carmichael, Cass.
- Timeline — replication studies in chronology.
- Original publications — full bibliography.
- FAQ · Glossary.
Footnotes
- Costa R, Dunsford M, Skagerberg E, et al. Psychological support, puberty suppression and psychosocial functioning. J Sex Med. 2015;12(11):2206–14.
- Carmichael P, Butler G, Masic U, et al. Short-term outcomes of pubertal suppression in a selected cohort of 12 to 15 year-olds with persistent gender dysphoria in the UK. PLOS ONE. 2021;16(2):e0243894.
- Costa R, Carmichael P, Colizzi M. To treat or not to treat: puberty suppression in childhood-onset gender dysphoria. Nat Rev Urol. 2016;13(8):456–62.