Selective serotonin reuptake inhibitors and Alzheimer's disease.

Given the failure to develop disease-modifying therapies for Alzheimer's disease (AD), strategies aiming at preventing or delaying the onset of the disease are being prioritized. While the debate regarding whether depression is an etiological risk factor or a prodrome of AD rages on, a key determining factor may be the timing of depression onset in older adults. There is increasing evidence that untreated early-onset depression is a risk factor and that late-onset depression may be a catalyst of cognitive decline. Data from animal studies have shown a beneficial impact of selective serotonin reuptake inhibitors on pathophysiological biomarkers of AD including amyloid burden, tau deposits and neurogenesis. In humans, studies focusing on subjects with a prior history of depression also showed a delay in the onset of AD in those treated with most selective serotonin reuptake inhibitors. Paroxetine, which has strong anticholinergic properties, was associated with increased mortality and mixed effects on amyloid and tau deposits in mice, as well as increased odds of developing AD in humans. Although most of the data regarding selective serotonin reuptake inhibitors is promising, findings should be interpreted cautiously because of notable methodological heterogeneity between studies. There is thus a need to conduct large scale randomized controlled trials with long follow up periods to clarify the dose-effect relationship of specific serotonergic antidepressants on AD prevention.