We set out to accomplish the following: (1) verify independent associations between e-cigarette use and depression, depression and inflammation, e-cigarette use and inflammation; (2) assess whether among all current e-cigarette users, odds of depression varies by stratified CRP level; (3) investigate whether the association between different categories of e-cigarette use (e.g., exclusive e-cigarette users, dual users, etc.)and depression varies by stratified CRP level; and (4) determine whether inflammation moderates the association between e-cigarette use and depression. The gene discussed is CRP; the disease is major depressive disorder.