BACKGROUND: Existing instruments used in health economics to measure health-related quality of life (HRQoL) have been criticized as they might not sufficiently reflect the HRQoL impacts of mental health problems. Our study investigates mental health patients' experiences of such impacts with a view to identifying potential domains that conventional HRQoL instruments might overlook. METHODS: Semi-structured, in-depth interviews were conducted with 16 participants receiving specialist mental health services in Norway. Interviews were analysed using reflexive thematic analysis. RESULTS: Five main themes were identified describing mental disorders' impact on patients' HRQoL: "Reduced functioning impacts", "Mental process impacts", "Social impacts", "Fragility", and "Sleep difficulty". While some overlap with conventional HRQoL instruments exists, distinct dimensions were identified, notably, "Fragility," encompassing unpredictability and inflexibility in daily life. CONCLUSIONS: The findings suggest that comprehensive assessment should consider broader mental health impacts beyond anxiety and depression, including cognitive difficulties, obstructive self-perception, and feelings of meaninglessness. Additionally, the impact of unpredictability on daily functioning and the role of sleep difficulties should be incorporated. These insights can inform the development of more patient-centred HRQoL measures for mental health populations, potentially leading to more accurate evaluation of mental health interventions.