77 Medical decision‑making competence regarding puberty suppression: perceptions of transgender adolescents, their parents and clinicians 5 INTRODUCTION The World Professional Association for Transgender Health (WPATH) Standards of Care (7th version) and the Endocrine Society clinical practice guideline on care for transgender children and adolescents recommend treatment with puberty suppression (PS; using gonadotropin-releasing hormone analogues (GnRHa)) provided that certain criteria are fulfilled4 (table 3 which can be found at page 14 shows the diagnostic criteria for treatment with PS for adolescents) (Coleman et al., 2012; Hembree et al., 2017). It is recommended to start PS when, among other criteria, adolescents suffer from an intense and long-lasting pattern of gender dysphoria/gender incongruence and after they first exhibit physical changes of puberty (at least Tanner stage 2). The aim of using PS in this context is to suppress, in a reversible manner, further development of secondary sex characteristics to allow the adolescent more time and rest to explore their gender before decisions are made on gender-affirming hormones (GAH) with more irreversible effects. Besides, it prevents psychological distress associated with the undesired endogenous pubertal development, as several adolescents stated in an interview study regarding the function of PS (Vrouenraets, de Vries, Hein, Arnoldussen, Hannema, & de Vries, 2022b). In addition, the physical outcome may be more satisfactory when using PS in the early stages of puberty because some surgeries, such as mastectomy, may then not be necessary or less invasive (i.e. periareolar rather than inframammary approach) because the development of secondary sex characteristics is prevented (van de Grift et al., 2020). Currently, the evidence base for the positive implications of treatment is still limited and treatment teams applying PS may experience feelings of unease (Vrouenraets et al., 2015). Their concerns regard the lack of data on its impact on physical, psychosocial, and cognitive development in the long-term, and the consequences for fertility (Chen et al., 2020; Laidlaw, van Meter, Hruz, van Mol, & Malone, 2019b). In an interview study, clinicians report worries about the risk of regret and the lack of long-term data on possible side effects of PS (Vrouenraets et al., 2015). Transgender adolescents themselves express some hesitations to start treatment with PS too, e.g. about the ability of adolescents to make informed decisions regarding medical treatment at the age of 12 or younger (Vrouenraets, Fredriks, Hannema, Cohen-Kettenis, & de Vries, 2016). Research shows that transgender people, after sex reassignment, have significantly higher risks for suicidal behaviour, psychiatric morbidity, and mortality compared to the general population (Dhejne et al., 2011; Wiepjes et al., 2020). Nevertheless, it is unknown whether these results are the same for transgender people who started treatment with PS in the early stages of their puberty. Besides, it is 4 According to the WPATH Standards of Care and the Endocrine Society clinical practice guideline, transgender adolescents undergo a diagnostic trajectory with a psychologist or psychiatrist over a longer period of time in order to assess eligibility for PS, discusses the benefits and potential risks of treatment, and be able to make a shared decision in a multidisciplinary team (adolescent, parents, clinicians).