Smoking and suicide
But the recent concern about onset of depression and suicidal thoughts among people quitting smoking (who presumably are in a frame of mind in which they want to live longer when they decide to quit) has led to renewed interest in the relationship between smoking and suicide. A recently published study by Professor Ronald Kessler (Harvard University) and colleagues provided some data and analysis relevant to this issue.
The study involved a survey of a representative sample of the adult American English-speaking population (n=5692). The study found that 2.6% had seriously thought about committing suicide in the previous year, 0.7% had made a plan of how they would do it, and 0.5% had made an attempt. This study, like many prior studies, found that smokers were about two or three times as likely to have thought about or attempted suicide in the past year than non-smokers. Heavy smokers were generally more likely to have thought about suicide than light smokers.
This survey also included a diagnostic interview for recent mental disorders. Like other studies, it found that people with virtually any mental disorder (from specific phobias to bipolar disorder) were more likely to be smokers, with the strongest relationship being for substance use (people with dependence on other substances being around 5 times more likely to be smokers than those not having a substance use disorder). People with a mental disorder were also more likely to have suicidal thoughts or attempts.
The study then examined whether smokers remained at greater risk of suicidal thoughts or attempts, after controlling for mental disorders. Controlling for mental disorders reduced the association between smoking and suicidal behavior to the point that it was no longer statistically significant.
My own interpretation of the data from this and other studies, is that mental disorders or some other factors of which mental disorders are highly correlated (e.g. mental health or general satisfaction with ones life) are a risk factor for both smoking and suicidal behavior. Thus people who as kids are unhappy and have difficulties dealing with their emotion are more likely to take up smoking, and more likely to become addicted to tobacco, and as adults are less able to quit smoking and are also, by virtue of their dissatisfaction with life, more likely to consider and attempt suicide.
Thus the relationship between smoking and suicidality is very unlikely to be causal. It is also worth noting that the size of the association is not very large. About one in 200 non-smokers attempt suicide each year and about one in 100 smokers attempt suicide each year.
None of this provides a direct explanation or helps us understand what may be going on when an individual attempts suicide in close proximity to a time when they had been trying to quit smoking (with or without using Chantix). But it does give us some idea of the frequency of certain events in the population. Around 45 million Americans smoke. At least 15 million of them make a quit attempt each year, and at least 5 million have already tried Chantix. This would imply that in the past year around 450,000 smokers made a suicide attempt, and possibly as many as 150,000 of them in the same year they made a quit attempt. Assuming around 2 million Chantix users in one year, and the same rate of suicide attempts per year as other smokers, this would lead us to expect around 20,000 smokers to make a suicide attempt in the same year they used Chantix, even if a quit attempt or Chantix use had no effect on risk for a suicide attempt. The precise number of events expected by chance will of course vary a bit according to the study one bases ones estimates on. But either way, one would expect a large number of cases by chance.
Now none of this means that making a quit attempt, or taking any particular medication, could or could not affect an individual’s risk for depression or suicide. That is a more complex question. But it does demonstrate that we might expect to hear of a large number of cases of suicide attempts by smokers taking any commonly used medicine, even if that medicine had no causal relationship with the suicide attempt.
The full text of the study by Kessler and colleagues can by accessed via the following link: