The Antidiabetic Metformin as a Novel Adjunct to Antidepressants in Major Depressive Disorder Patients

Selective Serotonin Reuptake Inhibitors (SSRIs) represent the standard treatment for Major Depressive Disorder (MDD). However, their efficacy is variable and incomplete. In order to explain, at least in part, such variable efficacy, we have shown that SSRI administration does not affect mood per se but, by enhancing neural plasticity, amplifies the influence of the living conditions on mood. Consequently, in a favorable environment, SSRI treatment leads to a reduction of symptoms while, in stressful conditions, it could lead to a worse prognosis. Here, we test the hypothesis that, given the clear association between living conditions and metabolic profile, the modulation of the latter may mimic the effect of the environment on SSRI outcome, determining treatment efficacy. Metformin is widely used as a first line treatment for patients with type 2 diabetes mellitus for more than 60 years for the reduction of hepatic glucose output and increase of the insulin mediated utilization of glucose. Previous studies demonstrated that metformin can rapidly cross the blood brain barrier and has several beneficial effects in the brain such as anti-inflammatory and neuroprotective effects. Furthermore, metformin, along with its anti-glycemic effects, has been documented to possess anti-depression effects in patients with type 2 diabetes. In Guo's study, 58 participants diagnosed with depression and type 2 diabetes were divided into two groups: one treated with metformin and the other with a placebo for 24 weeks. Analysis of MADRS and HRSD-17 scores showed that metformin significantly reduced MADRS scores and HRSD-17 scores. Metformin administration improves depressive symptoms in type 2 diabetes mellitus.