Objective: To test competing hypotheses that monotherapeutic antidepressant exposure is associated with an increased versus a decreased risk of dementia.

Methods: A prospective national matched cohort study from Israel (N = 71,515) without dementia (2002–2012) aged 60 and over were followed up for incident dementia from May 2013 to October 2017. Exposure to antidepressant monotherapy was classified with Anatomical Therapeutic Chemical Codes (N06A) from January 1, 2013 to December 31, 2016. The association between antidepressant monotherapy and the risk of incident dementia was quantified with hazard ratios (HR) and their 95% confidence intervals (CI) obtained from Cox regression models unadjusted and adjusted for 42 covariates. The robustness of the results was tested with 24 sensitivity analyses: 19 analyses restricted to subsamples with plausible differential dementia risks (e.g., anxiety and depression), and 5 analyses across and within antidepressant drug classes.

Results: In the primary analysis, the risk of incident dementia for the group exposed to antidepressant monotherapy compared to the group unexposed to antidepressants was estimated with an unadjusted HR = 4.09 (df = 1, 95% Wald CI = 3.64, 4.60) and an adjusted HR = 3.43 (df = 1, 95% Wald CI = 3.04, 3.88). Across the 24 sensitivity analyses the estimated adjusted HR values ranged from 1.99 to 5.47.

Conclusion: In this study, monotherapeutic antidepressant exposure in old age was associated with increased incident dementia. Clinicians, caregivers, and patients may wish to consider this potentially negative consequence of antidepressant exposure and aim to balance the costs and benefits of treatment.