Before reading the literature, the author believed any association of current smoking and suicidality would be due to selection bias; i.e., those who chose to smoke are a priori at greater risk to develop psychiatric illnesses, and not due to a causal effect of smoking. However, this selection bias (or smoking as a marker) explanation would posit that ex-smokers should also have increased risk of suicidality; this was not found. Although one could rationalize this by saying smokers who are able to quit are those with no or less psychiatric illnesses, one would still expect to see some increased suicidality in ex-smokers. In addition, the existence of a plausible biological mechanism; i.e., chronic smoking decreases serotonin and MAO and low levels of each are related to suicide makes a causal link possible. Thus, this author believes more direct and generalizable replications of low serotonin and MAO in smokers and their relationship to suicide are needed.
