OBJECTIVES: Research has shown that dialectical behaviour therapy (DBT) is effective in reducing self-harm and suicidal ideation, but there is also some evidence of negative effects with differences in the reports from clients and staff. However, no research has focused on both groups' understandings of negative effects. This study aimed to explore client and staff experiences of the negative effects from DBT, investigate how their understandings compare, and how staff address any negative effects that arise. METHODS: Eight client participants and seven staff participants, who had experienced or witnessed negative experiences from DBT, engaged in semi-structured interviews, the transcripts of which were analysed using reflexive thematic analysis. RESULTS: Four themes relating to client experiences were generated: 'I'm the problem', 'DBT can do no wrong', 'No understanding of trauma' and 'An unhealthy "blueprint for relationships"'. Five themes relating to staff experiences were generated: 'It's not me, it's the client', 'DBT or nothing', 'We don't do 'why' in DBT', 'We did make some changes' and 'Organisational "restrictions"'. CONCLUSIONS: Both staff and clients understood negative effects from DBT to include pathologisation and re-traumatisation. However, whilst clients related negative effects to the therapeutic relationship, staff highlighted the impact of organisational restrictions. The findings support a number of changes to practice, particularly the need to recognise potential negative effects and provide meaningful informed consent procedures.