Objectives The intent of a death from overdose can be difficult to determine. The goal of this study was to examine the association of psychiatric diagnoses among overdose deaths ruled by a medical examiner as intentional, unintentional and indeterminate intent.

Methods All Veterans Health Administration patients in Fiscal Year 1999 (n=3 291 891) were followed through Fiscal Year 2006. We tested the relative strength of association between psychiatric disorders among types of overdoses (categorised by intent) using multinomial models, adjusted for age, sex, Veterans Affairs priority status and Charlson comorbidity scores. Data were from National Death Index records and patient medical records.

Results Substance use disorders (SUD) had a stronger association with indeterminate intent overdoses than intentional overdoses (adjusted OR (AOR)=1.80, 95% CI 1.47 to 2.22). SUDs also had a stronger association with unintentional overdoses than intentional (AOR=1.48, 95% CI 1.27 to 1.72), but the reverse was true for all other psychiatric disorders (except post-traumatic stress disorder).

Conclusions Overdoses ruled indeterminate may be misclassified suicide deaths and are important to suicide surveillance and prevention efforts. Additionally, overdose deaths not classified as suicides may include some cases due to suicidal-like thinking without overt suicidal intent.