The duration of undiagnosed or untreated bipolar disorder (DUBD) has become a focus of research interest. However, its relationship with clinical characteristics and outcomes remains poorly understood.

The objective of this systematic review and meta-analysis was to examine DUBD and explore its relationships with clinical characteristics and outcomes in bipolar disorder.

We conducted a systematic search of the literature to identify studies reporting on DUBD and its relationships with clinical characteristics and outcomes including frequency of relapse into mood episodes, severity and persistence of mood symptoms, functional and cognitive measures, suicidality, hospital admission rate, and comorbidities such as substance use disorders.

Thirty articles met inclusion criteria for the systematic review, and 23 studies were included in the three different sets of meta-analyses. The pooled mean DUBD across all studies was 9.10 years. Early onset, depression as the polarity of the first mood episode, lifetime suicide attempts, comorbid anxiety and alcohol use disorders, and family history of bipolar disorder were associated with significantly longer DUBD, whereas diagnosis of bipolar I disorder and lifetime psychotic symptoms were associated with shorter DUBD. Studies that investigated outcomes subsequent to the diagnosis of bipolar disorder yielded conflicting results.

DUBD may be associated with certain adverse outcomes. This association indicates the importance of adopting a more comprehensive approach to assessing mood disorders, with an emphasis on prioritising early screening for bipolar disorder. The significant heterogeneity among included studies suggests a need for improved methodological rigour in future research.