A prognostic model predicted deterioration in health-related quality of life in older patients with multimorbidity and polypharmacy

•Multimorbidity and polypharmacy increase the risk of deterioration in quality of life.•First IPD-based quality of life prognostic model for older multimorbid patients.•Model performed well in terms of discrimination, calibration, and generalizability.•Baseline quality of life and functional status have the strongest prognostic power.•Quality of life/functionality appraisal might help identify high-risk patients.