Adolescent depression is a prevalent and disabling condition, but current psychological treatments are only moderately effective. One way to enhance outcomes is to further our understanding of adolescent depression and improve our capacity to target the most frequently reported and problematic symptoms. A common but often neglected symptom of depression is fatigue, which is associated with considerable impairment and has the potential to interfere with adolescents’ engagement in psychological therapies. Despite this, the experience of fatigue in adolescent depression and how we target it in treatment is currently poorly understood. Therefore, we aimed to explore adolescents’ experiences and understandings of fatigue in depression, recruiting from clinical and community settings. Semi-structured interviews were conducted with 19 UK-based adolescents aged 14–18 years old with elevated symptoms of depression. Using reflexive thematic analysis, three themes were generated.Fatigue is a complex conceptexplored adolescents’ understanding of fatigue as a dynamic, multifaceted symptom which had mental and physical components.Trapped in a cycle of fatigueconsidered the complex and reciprocal relationship between fatigue and other depressive symptoms, and the subsequent impact of limited energy on engagement with everyday activities. Finally,stigma as a barrier to help-seekinghighlighted how adolescents were reluctant to seek help due to experienced stigma and the perception that fatigue was not a serious enough symptom. Findings from this study suggest that fatigue should be viewed as a psychological as well as somatic symptom of depression, with implications regarding the identification and treatment of fatigue in depression in routine clinical practice.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00787-023-02243-3.