To determine the costs associated with antidepressant (AD) use and mental health status.

Data were obtained from a population-based health survey of 2,004 older adults. Depression and anxiety were based on DSM-IV criteria and measured at two time points 1 year apart. AD use and health service use and costs were identified from provincial administrative databases. Patient costs included drug copayments, transportation and time spent seeking medical care. Costs associated with AD use were studied as a function of mental health status at baseline and follow-up interviews [i.e. persistence, incidence, remission, no illness]. Generalized linear models with a gamma distribution (log link) were used to control for potential confounders such as socio-economic and clinical factors and AD adherence rates.

The costs incurred by participants using AD (16.6%) reached $6861 (95% CI: $5586, $8426), significantly more than costs for those not using AD: $4662 ($3679, $5908). AD use was associated with increased total adjusted costs in respondents with no depression and anxiety and in respondents with incident anxiety. Increased costs were due to significantly higher hospitalisation and outpatient costs. The results also suggested a negative association between adherence to AD and the persistence of depression.

The results did not show important cost savings or decreased health service use associated with AD use and this for all depression and anxiety groups. Future cost studies may consider the analyses of different AD classes with respect to the different clinical mental health profiles in older adults.