OBJECTIVESThis study employed a national longitudinal cohort to assess expected years of life lost (EYLL) in newly diagnosed psychiatric patients.METHODSData from Taiwan's National Death Registry and Health Insurance Research Database were scrutinized to identify patients with various psychiatric disorders. Disorders were ranked hierarchically, and age groups were categorized as young, middle-aged, and older adults. We utilized the semiparametric survival extrapolation method to estimate life expectancy (LE) and EYLL. Modifying effect of comorbid conditions and socioeconomic characteristics were also explored.RESULTSAmong the 5,757,431 cases, young adults with dementia, alcohol use disorder, schizophrenia, and bipolar disorder experienced an excess of 15 years of EYLL. Middle-aged adults faced approximately 9 years or more of EYLL, while older adults had lower EYLL values. Comorbid conditions, low income levels, and living in rural areas were associated with higher EYLL.CONCLUSIONSThis study underscores the substantial EYLL among young adults with psychiatric disorders and the significant impact of specific disorders on EYLL. Early intervention, tailored support, and healthcare system readiness are imperative for improved outcomes. Resource allocation and targeted interventions focusing on early detection and comprehensive treatment can alleviate the economic burden.