Possible mechanisms through which antidepressants may increase the risk of AD and related dementias

MechanismDescription
Immune-inflammatory dysregulationDrug-induced reduction in levels of anti-inflammatory cytokines (IL-4, IL-10, and IL-13); stimulation of NK and B cell activity; shift in microglial activation towards a neuroinflammatory phenotype
Increased risk of infectionPossible immunosuppressive effect caused by reductions in CRP, IL-6, and TNF-α; reduction in white cell count; reduction in CD4+ count
Gut-brain dysbiosisDrug-induced reduction in gut commensals and increase in pro-inflammatory bacteria in animal models; antibacterial effect on common gut commensals in vitro, including on beneficial species such as Lactobacillus
Stress axis dysfunctionFailure to normalize HPA axis dysfunction; reduced effectiveness in the presence of HPA axis dysregulation; persistence of ongoing stressors despite relief of depressive symptoms
OthersPossible acceleration of normal aging in animal models; possible changes in cerebral microvasculature leading to local ischemia; suppression of REM sleep and precipitation of REM sleep behavior disorder

CRP: C-reactive protein