OBJECTIVES: Expenditures on antidepressants in Canada are rapidly increasing; yet few studies have analyzed the characteristics of antidepressant users. This study investigated the prevalence and incidence of antidepressant use in British Columbia over eight years. METHODS: Antidepressant utilization and demographic data were assessed for the population of British Columbia from 1996 to 2004. Prescription claims were identified within the PharmaNet database for serotonin reuptake inhibitors (SSRI), tricyclics, monoamine oxidase inhibitors, bupropion (categorized separately for smoking cessation), and "novel" antidepressants, such as venlafaxine. Incident utilization (dispensed "first" antidepressant after two years without an antidepressant claim) and prevalent utilization were analyzed. All cohort members were required to have continuous registration with British Columbia medical services for at least two years before the first antidepressant claim. RESULTS: Prevalence of antidepressant use doubled, from 34 to 72 users per 1,000 population, between 1996 and 2004. The prevalence of particular classes of antidepressants also changed over time. Prevalence of novel antidepressants and SSRIs increased, although incidence of SSRIs decreased. Prevalent and incident use of bupropion for smoking cessation peaked in 1999 but then declined. Quarterly incident antidepressant use increased in 1998 and 1999 (6.5 and 11.3 users per 1,000) but decreased through 2004 (4.2 users per 1,000). Those aged 20 to 44 years and those aged 45 to 64 years showed the greatest peak in incident antidepressant use. A socioeconomic gradient in prescribing was observed. CONCLUSIONS: Prevalent antidepressant use has increased dramatically since 1996. By contrast, incident use increased from 1998 to 1999 but then decreased through 2004. Many complex factors likely contribute to antidepressant prescribing patterns.