Overall, the results showed that smokers showed declines in emotional stability, extraversion, openness, agreeableness and conscientiousness, relative to non-smokers. However, the precise patterns of change varied across the different samples. The most consistent pattern was for smokers to show relative declines in emotional stability and extraversion.

Stephan and his team also looked to see if stopping smoking had any positive personality consequences. In fact, there was little evidence of this. If anything, stopping smoking was associated with declines in agreeableness. Perhaps, the researchers speculated, this is because of a loss of “smoking-related social interactions”; residual adverse effects of smoking; and due to health-related side-effects associated with smoking cessation, such as “heightened risk of obesity and type 2 diabetes” both of which are known to have unhelpful consequences for personality traits.