PURPOSE: This paper presents independent associations between complex multimorbidity and health-related quality of life using the EQ-5D-5L instruments. Identifying the decrements in utility associated with complex multimorbidity is of value for economic evaluation and health technology assessment.

METHODS: Data from the population normative dataset from the Irish EQ-5D-5L study were combined with baseline data from the SPPiRE (Supporting Prescribing in Older Adults with Multimorbidity in Irish Primary Care) randomised controlled trial. The trial included an Irish cohort aged 65+ with complex multimorbidity. For the analysis, the estimation sample consisted of 364 individuals from the SPPiRE complex multimorbidity sample, along with 116 individuals aged 65+ from the general population who did not report having any serious illness. A multivariate ordered probit regression model was used to estimate the independent associations between complex multimorbidity and the five EQ-5D-5L dimensions.

RESULTS: Complex multimorbidity was independently associated with a lower probability of reporting no problems for all five EQ-5D-5L dimensions, and a higher probability of reporting the most extreme response for all five dimensions. The loss in health utility associated with complex multimorbidity was estimated to be − 0.506 (95% CI − 0.567, − 0.445) relative to those aged 65 years and over with no serious illness. The negative health impact was most pronounced for pain/discomfort and anxiety/depression.

CONCLUSION: This study reported the associative impacts of complex multimorbidity for all EQ-5D-5L dimensions and for health utility overall. The findings highlight the potential impact on health-related quality of life of interventions that can prevent or delay the onset and progression of multimorbidity.