BACKGROUND: Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder that can persist into adulthood. Young people often stop taking ADHD medication during adolescence despite evidence that continuation would be beneficial. Increasingly, young people are restarting medication in early adulthood suggesting that cessation was premature. In this paper we explore the reasons given by young people for discontinuing ADHD medication. METHODS: Qualitative data from the Children and Adolescents with ADHD in Transition between Children's and Adult Services (CATCh-uS) project was analysed to look for reasons for stopping medication. Semi-structured interviews with three groups of young people were analysed using thematic and framework analysis; this included young people prior to transition (n = 21); young people that had successfully transitioned to adult services (n = 22); and young people who left children's services prior to transition but re-entered adult services later (n = 21). RESULTS: Reasons given by young people for stopping ADHD medication included the following: the perceived balance between benefits and adverse effects of medication; perceptions of ADHD as a childhood or educational disorder; life circumstance of the young person and challenges young people faced in accessing services. CONCLUSIONS: A multidimensional approach is needed to address discontinuation of ADHD medication in order to improve the long-term prospects and quality of life for these young people. Possible approaches include access to non-pharmacological treatments and improved psychoeducation. As many reasons given by young people are not unique to ADHD, these findings are also of relevance to medication adherence in other chronic childhood conditions.