In a study conducted on 341 subjects, which combined major depressive disorder and nicotine dependence, it was shown that depressed smokers had significantly higher levels of nitric oxide metabolites (NOx), fibrinogen, high-sensitivity C-reactive protein (hs-CRP), and AOPPs, and lower levels of total reactive antioxidant potential (TRAP), compared to non-depressed patients who had never smoked [15]. Here, CRP is linked to major depressive disorder.