In terms of actual data, many lines of evidence indicate smoking causes a physical dependence on nicotine and this results in a withdrawal syndrome (Hughes 2007a) that includes worsened mood and other behaviors that would increase the risk of suicide (Hughes 2007b). Many studies have found that negative affect symptoms are the most common symptoms of tobacco withdrawal (Hughes 2007b) and several studies suggest smoking cessation can precipitate a clinical depression in a subset of smokers (Hughes 2006). Thus, increased suicidal behavior early on after cessation due to nicotine withdrawal is clearly plausible. In contrast, most data indicate that prolonged abstinence for months or years (i.e. well after withdrawal is abated) is associated with less, not more, depressed mood (US Department of Health and Human Services 1990a).
