Effects of Cigarette Smoking on Neuropsychological Performance in Mood Disorders: a Comparison Between Smoking and Nonsmoking Inpatients

Objective: To investigate the effects of cigarette smoking on neuropsychological performance in patients with mood disorders.

Method: One hundred depressed patients with DSM-IV-TR-defined major depressive disorder (n = 61) or bipolar disorder (n = 39), hospitalized for a 4-week psychiatric rehabilitation program, were included. Forty-five were active regular smokers, and 55 were nonsmokers who had never smoked in their lifetime. At the beginning and the end of the hospitalization, patients were administered a comprehensive neuropsychological battery (evaluation of verbal and visual memory, working memory, attention, visual-constructive ability, language fluency, and comprehension) as primary outcome measures and psychometric scales (evaluation of depression and illness severity). Smoking status was assessed by personal interviews. Investigators were blind to the results of neuropsychological tests and to the smoking status of the patients. Data were collected from February 2011 to January 2012.

Results: At the beginning of the hospitalization, smokers showed significantly better performance in verbal memory, language fluency, and working memory (all P values < .01) than nonsmokers. No interaction between smoking and diagnosis was found. At the end of the hospitalization, the whole group of patients significantly improved in several cognitive domains, with smokers maintaining significantly better performance in verbal memory, language fluency, and working memory (all P values < .01) than nonsmokers.

Conclusions: Our preliminary results indicate a better performance by smokers in verbal memory and working memory domains than by nonsmokers, suggesting that a cognitive enhancement may be associated with nicotine use in depressed patients with MDD or bipolar disorder. Smoking may be a form of cognitive self-medication mediating the association between smoking and mood disorders. Further studies with larger samples are needed.