Importance: In recent decades, there has been increased interest in the possible adverse neurological effects of 5α-reductase inhibitors (5-ARIs), which have been used mainly for benign prostatic hyperplasia and androgenic alopecia. Numerous studies and reports have indicated associations of 5-ARIs with depression and suicide. However, most of these studies had methodological shortcomings, and very little is known about the potential association of 5-ARIs with dementia.
Objective: To investigate the association of 5-ARI use with all-cause dementia, Alzheimer disease, vascular dementia, depression, and suicide.
Design, setting, and participants: This Swedish register-based cohort study included 2 236 876 men aged 50 to 90 years between July 1, 2005, and December 31, 2018. Statistical analyses were performed from September 15, 2021, to May 25, 2022.
Main outcomes and measures: A diagnosis of all-cause dementia, Alzheimer disease, vascular dementia, depression, or completed suicide.
Exposures: A recorded prescription in the Swedish national prescription register of finasteride or dutasteride and duration of use.
Results: Of 2 236 876 men (median age at the start of follow-up, 55 years [IQR, 50-65 years] and at treatment initiation, 73 years [IQR, 66-80 years]), 70 645 (3.2%) started finasteride treatment, and 8774 (0.4%) started dutasteride treatment. Men taking finasteride or dutasteride were at increased risk of all-cause dementia (finasteride: hazard ratio [HR], 1.22 [95% CI, 1.17-1.28]; dutasteride: HR, 1.10 [95% CI, 1.01-1.20]), Alzheimer disease (finasteride: HR, 1.20 [95% CI, 1.10-1.31]; dutasteride: HR, 1.28 [95% CI, 1.09-1.50]), vascular dementia (finasteride: HR, 1.44 [95% CI, 1.30-1.58]; dutasteride: HR, 1.31 [95% CI, 1.08-1.59]), and depression (finasteride: HR, 1.61 [95% CI, 1.48-1.75]; dutasteride: HR, 1.68 [95% CI, 1.43-1.96]). However, the magnitude of the association decreased over time, and the findings became statistically nonsignificant with continuous exposures over 4 years, except for depression, which showed a constant risk over time, with no differences between finasteride and dutasteride. In contrast, 5-ARIs were not associated with suicide (finasteride: HR, 1.22 [95% CI, 0.99-1.49]; dutasteride: HR, 0.98 [95% CI, 0.62-1.54]).
Conclusions and relevance: This cohort study found that, while men receiving 5-ARI treatment showed a higher risk for dementia in the initial periods after starting treatment, the decreasing magnitude of the association over time suggested that the risk may be, entirely or in part, due to increased dementia detection among patients with benign prostate enlargement. Both finasteride and dutasteride were similarly associated with depression with a constant risk over time, while neither drug was associated with suicide. Prescribing clinicians and potential users should be aware of the possible risks for depression associated with 5-ARI use.