Smoking and Depression: A Co-morbidity

Substance use disorders and psychiatric disorders co-occur frequently. The prevalence of smoking increases dose-dependently with the number of psychiatric diagnoses. The aim of this article is to review the relationship between smoking and depression. A PubMed literature search limited to the last 10 years was conducted with the terms smoking and depression. Some earlier papers that exerted an impact on future studies were also included. Results strongly show that depression (defined as depressive mood, major depressive disorder, or negative affect) increases the risk of smoking and that smoking increases the risk of depression. The relationship between depression and smoking cessation is less evident, as some clinical and epidemiological studies have indicated an effect of depression on ability to quit whereas other studies have not. Research has also strongly suggested that commonality in genetic and environmental factors underlies the co-morbidity of smoking and depression, although the specific mechanisms remain to be identified. The relationship between depression and smoking is firmly established. Reciprocal relationships between depression and smoking cessation are strongly suggested, but this clinically and theoretically significant link needs further clarification.