Substance use among older adults with bipolar disorder varies according to age at first treatment contact.

Background: The use of alcohol and drugs is common among people with bipolar disorder, but it is unclear if age of onset modifies this association.
Aims: To determine the cross-sectional and longitudinal association between age of onset of bipolar disorder (BD) and disorders associated with the use of alcohol or other substances in later life, as well as their impact on mortality.
Methods: Cohort study of a community-representative sample of 38,173 men aged 65-85 years at the start of the follow up period of 18 years. We used the Western Australian Data Linkage System to ascertain the presence of BD and substance use disorders according to the International Classification of Diseases (ICD). We also collected information on concurrent morbidities: diabetes, hypertension, ischaemic heart disease and stroke.
Results: 175 men had BD onset < age 60 years and 75 ≥ 60 years. Compared with older men without BD, the adjusted odds of alcohol use disorders were 3.87 (95%CI = 2.52, 5.93) for men with BD onset < 60 years and 2.38 (95%CI = 1.08, 5.25) for those with onset ≥ 60 years. The adjusted hazard ratio of incident disorders associated with the use of alcohol and other substances was 3.23 (95%CI = 1.87, 5.58) and 2.38 (95%CI = 1.38, 4.11) respectively for men with BD onset < 60 years. BD with onset ≥ 60 years was not associated with substance use disorders. The mortality hazard was not affected by the interaction between BD and the use of substances.
Conclusions: Substance use disorders (alcohol or others) are more prevalent among older adults with than without BD, but new cases are only more frequent among men with BD onset < 60 years of age. Grouping BD into early and late onset is clinically informative and may affect approach to assessment and management.
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