Background The scrutiny surrounding gender-affirming medical treatment (GAMT) for youth has increased, particularly concerning the limited evidence on long-term treatment outcomes. The Standards of Care 8 by the World Professional Association for Transgender Health addresses this by outlining research evidence suggesting “effective” outcomes of GAMT for adolescents. However, claims concerning what are considered “effective” outcomes of GAMT for adolescents remain implicit, requiring further reflection. Methods Using trans negativity as a theoretical lens, we conducted a theory-informed reflexive thematic analysis of the (...) literature cited in the “Research Evidence” section of the SOC8 Adolescents chapter. We selected 16 articles that used quantitative measures to assess GAMT outcomes for youth, examining how “effective” outcomes were framed and interpreted to uncover implicit and explicit normative assumptions within the evidence base. Results A total of 44 different measures were used to assess GAMT outcomes for youth, covering physical, psychological, and psychosocial constructs. We identified four main themes regarding the normative assumptions of “effective” treatment outcomes: (1) doing bad: experiencing distress before GAMT, (2) moving toward a static gender identity and binary presentation, (3) doing better: overall improvement after GAMT, and (4) the absence of regret. These themes reveal implicit norms about what GAMT for youth should achieve, with improvement being the benchmark for “effectiveness.” Discussion We critically reflect on these themes through the lens of trans negativity to challenge what constitutes “effective” GAMT outcomes for youth. We explore how improvement justifies GAMT for youth and address the limitations of this notion. Conclusions We emphasize the need for an explicit discussion on the objectives of GAMT for adolescents. The linear narrative of improvement in GAMT for adolescents is limited and fails to capture the complexity of GAMT experiences. With currently no consensus on how the “effectiveness” of GAMT for adolescents is assessed, this article calls for participatory action research that centers the voices of young TGD individuals. (shrink)