Association of smoking and nicotine dependence with severity and course of symptoms in patients with depressive or anxiety disorder.

BACKGROUND: Previous research has indicated a strong association of smoking with depression and anxiety disorders, but the direction of the relationship is uncertain. Most research has been done in general population samples. We investigated the effect of smoking and nicotine dependence on the severity and course of depressive and anxiety symptoms in psychiatric patients.
METHODS: Data came from the Netherlands Study of Depression and Anxiety (NESDA) including participants with a current diagnosis of depression and/or an anxiety disorder (N=1725). The course of smoking status and symptoms of depression, general anxiety, social anxiety, and agoraphobia were measured at baseline and after one and two years. Age, gender, education, alcohol use, physical activity, and negative life events were treated as covariates.
RESULTS: At baseline, the symptoms of depression, general anxiety, and agoraphobia were more severe in nicotine-dependent smokers than in never-smokers, former smokers, and non-dependent smokers. These differences remained after adjusting for covariates. Smaller differences were observed for severity of social anxiety which were no longer significant after controlling for covariates. Over a two-year follow-up, the improvement of depressive and anxiety symptoms was slower in nicotine-dependent smokers than in the other groups even after controlling for covariates. There were no differences between the groups in the course of symptoms of social anxiety and agoraphobia over time.
CONCLUSIONS: In psychiatric patients, smoking is associated with higher severity of depressive and anxiety symptoms, and with slower recovery, but only when smokers are nicotine-dependent.