Background: Although addiction therapists are faced with immense pressures to effectively support clients through relapses and overdose risks, the evidence base on relapse remains significantly limited. Aims: This study aims to generate novel understandings of substance misuse relapse from a lived experience perspective of addiction therapists. Methods: Data were generated through semi-structured interviews with seven addiction therapists across specialist addiction treatment services in England, and subsequently analyzed using interpretative phenomenological analysis. Findings: The analysis revealed three superordinate themes around the impact that supporting clients through relapse has on addiction therapists’ psychological wellbeing, their treatment approaches, and their therapeutic relationships. Conclusion: Relapse can shape how therapists perceive and engage with recovery of their clients. Although therapists sometimes consider relapse as a positive experience, they often feel negative psychological effects from it, including emotional withdrawal, self-doubt, and compassion fatigue. This paper sets out the implications for policy, practice, and research.