Treating substance misuse in hospital places a considerable burden on patients and on the healthcare system. The cost of treatment and hospital stays for patients with substance use disorders is substantial. We examined the factors associated with the length of stay in hospital for such patients across four age cohorts in the USA by using the 2004 Nationwide Inpatient Sample (www.hcup-us.ahrq.gov/nisoverview.jsp).

The admission source and disposition type for patients with substance misuse differed by age cohort. A significantly larger proportion of older adult patients were admitted from the emergency room than were their younger counterparts. Higher proportions of young and middle-aged patients left the hospital against medical advice than did their older counterparts. Across all four age cohorts, the majority of patients admitted to hospital for substance use disorders were male and lived in an area with median household income less than US$60 000 (£39 000).

Income level was a significant factor associated with hospital length of stay for elderly patients with substance use disorders. Most of the elderly patients were insured by Medicare (health insurance for people age 65 or older, managed by the federal government), thus income became a significant factor in addition to their Medicare coverage. Low-income elderly patients could be financially disadvantaged in out-of-pocket spending for mental health services. Previous research indicates that low-income elderly people are worse off financially than non-elderly adults (aged <65) in the same poverty class and than their elderly peers in other poverty classes. ^{Reference Xu1} Underinsured adults are more likely to forgo needed care than those with more adequate coverage and have rates of financial stress similar to those who are uninsured. ^{Reference Ross, Bradley and Busch2}

Non-elderly Medicaid (jointly funded, federal/state health insurance programme for people on low incomes and with various needs) patients had significantly longer hospital lengths of stay than their counterparts with commercial insurance. Recent research indicates that Medicaid recipients with substance use disorders were less likely to use community services. ^{Reference Clark, Samnaliev and McGovern3} Research based on the National Household Survey on Drug Abuse ^{Reference Adelmann4} indicates that the rates of substance use disorder are much higher among Medicaid recipients than among most other health insurance groups. Psychiatric disorders and substance misuse are major problems for the Medicaid population. Therefore, efforts to promote detection and treatment of these disorders in this group should focus on reducing barriers to education, family stability and departure from welfare. ^{Reference Adelmann4}

The study was limited to community hospitals across the USA, therefore the analysis does not include specialty psychiatric or substance misuse treatment facilities. However, it helps us to better understand the relationship between age cohorts and hospital treatment for substance use disorders, and provides a rationale for further exploration of the key factors associated with the most efficient care for adult patients with substance use disorders.