Multi-morbidity in Physical Illness and Co-occurring Mental Illness and Substance Use Disorders: Who are at Risk?

BACKGROUND: Multi-morbidity defined as the co-existence of two or more chronic conditions in the same individual is very common, particularly among individuals at risk for mental illness (MI) and Substance Abuse Disorders (SUD). Multi-morbidity presents challenges to treatment planning, management, service delivery, quality of healthcare and outcomes.

OBJECTIVE: Identify subgroups of veterans with multi-morbidity (diabetes, heart disease, and hypertension) who are at risk for different types of MI and SUD.

METHODS: Longitudinal data (2002-2003) of Veteran Health Administration and Medicare claims on veterans with diabetes, heart disease, and hypertension(N = 1.396 million); these conditions, types of MI and SUD were identified using International Classification of Diseases, 9th edition codes. Chi-square tests and multinomial logistic regressions were performed to analyze the relationship between multi-morbidity and co-occurring MI and/or SUD.

FINDINGS: We categorized veterans into 15 mutually exclusive groups of co-occurring MI and SUD based on a hierarchical scheme. Overall, individuals with all three conditions (diabetes, heart disease, and hypertension) had higher rates of mental illness and/or SUD (37%) compared to those with only one chronic physical condition(34%). Rates of affective disorders (bipolar and major depression) were almost twice more likely in those with multi-morbidity. Women, Caucasians, younger, and not-married were at greater risk for co-occurring MI and/or SUD.

CONCLUSION: Multi-morbidity is associated with high rates of MI and SUD.

IMPLICATION: Presence of individuals with multiple medical conditions and MI and/or SUD suggest higher expenditures, adverse interactions due to poly-pharmacy and the need for coordinated care between primary and MI/SUD care.