Depression is associated with an increased frequency of smoking. Addicted smokers are characterized by preoccupation with smoking, abnormal attachment to cigarettes and anticipation of brain reward from the drugs in cigarette smoke. Attempts to quit smoking often lead to a decreased level of pleasure and undesirable mood swings. Thus, once the brain has adapted to the daily dose of the drug, it seems abnormal to the brain if the user attempts to abstain.

Individuals with underlying or current depressive symptoms are more likely to experience mood disturbances when they attempt to quit. Furthermore, it appears that smoking may mask an underlying depression in some smokers.
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