Background: Depression and anxiety is prevalent among patients with dementia but the extent to which these conditions are treated with antidepressants has not previously been investigated.

Methods: Nationwide register-based data in Denmark were used to identify all patients diagnosed with dementia or osteoarthritis at hospital admission or at first outpatient contact during the period 1995–2000. Rates of subsequent purchase of antidepressants from pharmacies were then calculated. Further, the rate of antidepressant use for patients with dementia was compared with the rate in a gender-, age-, and calendar-matched sample of the general population.

Results: In total, 24,137 patients with a main diagnosis of dementia and 100,378 patients with a main first diagnosis of osteoarthritis were incorporated in the study. A total of 43.2% of patients with dementia received antidepressants during follow-up compared to 16.0% of patients with osteoarthritis. Among patients with a diagnosis of dementia, the rate of subsequently purchasing antidepressants was 4.17 times higher (95% CI = 4.05–4.29) than that of patients with a first diagnosis of osteoarthritis, and 8.85 times higher (95% CI = 8.68–9.03) than that of a gender-, age- and calendar-matched sample of the general population. The rate was increased in all subgroups of patients regardless of gender, age, socio-economic group and time since diagnosis.

Conclusions: The findings challenge the widely held contention that depression and anxiety in patients with dementia is underdiagnosed and undertreated in clinical practice.