Mixed-effects models reveal prediction of long-term outcome by duration of untreated psychosis (DUP) and illness (DUI) varies with quantile gradation but is invariant with time across 7 years in the Cavan-Monaghan First Episode Psychosis Study (CAMFEPS).

While associations between duration of untreated psychosis (DUP) and outcome have been widely reported, how long these relationships endure following initiation of treatment and how such associations are distributed across the range of DUP values encountered remain unclear. This study investigates prospectively (i) whether prediction of outcome by DUP and by duration of untreated illness (DUI) diminishes, remains stable or increases in the long term after initiating treatment, and (ii) whether these relationships for differing indices of outcome vary across gradations of DUP-DUI values. Sixty-two subjects were evaluated prospectively for DUP, DUI, premorbid features, psychopathology and quality of life at both first episode psychosis (FEP) and at 7-year follow-up; functionality and service engagement were assessed at follow-up. Data were analysed using mixed-effects models for DUP and DUI quantiles. Prediction by longer DUP and DUI of greater psychopathology, particularly negative symptoms, and lower quality of life remained stable between FEP and follow-up; longer DUP and DUI also predicted lower functionality and service engagement at follow-up. While most associations were confined to the longest DUP-DUI quartile, those between DUP-DUI and negative symptoms and quality of life were distributed in a graded manner across DUP-DUI quartiles. Material confounding with premorbid features, including lead-time bias, was not supported. These findings suggest that benefits of reducing DUP-DUI may endure for at least a decade beyond FEP and that even modest reductions in DUP-DUI may confer particular advantage in the more debilitating and intransigent domain of impairment.