Antidepressants account for the causal effect of major depressive disorder on type 2 diabetes

Background: Patients with major depressive disorder (MDD) face an elevated risk of type 2 diabetes (T2D). However, the contribution of the disease itself versus the side effects of antidepressants to this increased risk remains unclear. Objective: This study aimed to investigate the overall and independent effects of MDD and exposure to antidepressants on T2D risk. Methods: Summary genome-wide association study datasets were utilized for the Mendelian randomization (MR) and multivariable MR (MVMR) analyses, including ones for MDD (N = 500,199), antidepressants (N = 175,161), and T2D (N = 933,970). Bayesian colocalization analysis was used to reveal shared genetic variation between MDD, antidepressants, and T2D. Results: We found that both MDD (OR: 1.15, CI: 1.03–1.30, P = 0.016) and antidepressants (OR: 1.37, CI: 1.22–1.53, P = 2.75E-08) have overall causal effects on T2D. While T2D was associated with the risk of antidepressant use (OR: 1.08, CI: 1.06–1.11, P = 8.80E-10), but not with the risk of MDD (OR: 1.00, CI: 0.98–1.01, P = 0.661). Our MVMR analysis showed that the use of antidepressants is associated with higher risks of T2D (OR: 1.21, CI: 1.07–1.37, P = 7.19E-04), while MDD is not linked to the risk of T2D (OR: 1.01, CI: 0.86–1.18, P = 0.799). Colocalization analysis identified two shared genetic loci between antidepressants and T2D. Conclusions: The elevated T2D risk in MDD patients is chiefly caused by antidepressant use. These findings emphasize the importance of considering the impact of antidepressants on metabolic health in individuals with MDD.