Which Came First, the Cigarette or the Psychiatric Diagnosis?

A greater proportion of individuals with psychiatric illness smoke tobacco compared to the general population. Over the last decade, the smoking prevalence in the general population has decreased to and then remained less than 20% while the smoking prevalence among individuals with bipolar disorder or schizophrenia has remained high at approximately 50% and 66%, respectively.  It has been increasingly recognized that individuals with serious mental illnesses experience a shortened lifespan of on average 10 years, largely due to premature mortality from tobacco-attributable illnesses.

Recent clinical research has consistently demonstrated the safety and effectiveness of use of anti-smoking medications in individuals with serious mental illness, giving clinicians the evidence base to confidently address and treat smoking in patients and help patients achieve a goal of successfully quitting smoking. The high prevalence and known benefits of quitting smoking provide psychiatrists with the opportunity to help improve the well-being and overall health of patients by treating smoking.

Many adult smokers with psychotic illnesses actually started smoking years before the onset of psychosis. This observation led researchers to investigate if smoking precedes psychotic illnesses and whether smoking could be part of the cause of psychotic illnesses. Despite well-known facts of smoking causing many illnesses such as cardiovascular diseases and cancers, some may be skeptical about the idea of cigarette smoke being part of the cause of a complex psychiatric illness such as schizophrenia. However, there are models for thinking about substances contributing to either onset of a psychiatric illness—such as the association between cannabis and incident psychotic illness—or to a worsening course of the illness—such as the way alcohol can perpetuate depressive symptoms in an individual with major depressive disorder and alcohol use disorder.

Is it possible cigarette smoke could have a similar effect in schizophrenia? Could cigarette smoke be associated with the onset of psychotic illnesses? Recent studies have addressed these questions.

A study by Kendler and colleagues involving 1.4 million Swedish women and 230,000 Swedish men addressed the association between smoking and schizophrenia. The investigators measured smoking status during pregnancy in women or during military service in men and found that smoking at baseline was associated with greater risk of onset of schizophrenia in women and men in a dose-response manner.  Furthermore, the investigators tested whether smoking was occurring during the prodrome of schizophrenia by looking at duration between baseline smoking and onset of schizophrenia. They found equally strong associations between smoking and schizophrenia in shorter- and longer-term follow-up groups, suggesting that baseline smoking did not represent smoking during the prodrome of schizophrenia. Since lower socioeconomic status is associated with smoking and with schizophrenia, the investigators measured and controlled for socioeconomic status and found only slight changes in strength of association between smoking and schizophrenia onset.  The authors discussed how these findings make it unlikely that the elevated smoking prevalence among those with schizophrenia could be explained by schizophrenia symptoms or treatments, and that it is much more likely that smoking precedes, and increases risk of, schizophrenia onset.

A recent meta-analysis explored these findings of smoking preceding schizophrenia in clinical studies. The authors’ review of 61 published prospective studies revealed smoking occurred in more than half of people presenting for their first episode of treatment for a psychotic illness.  Additionally, daily smoking was associated with greater risk and earlier age of onset of psychosis compared with those who were nonsmokers.

These studies can inform clinicians that, in general, schizophrenia does not cause individuals to smoke, and that the majority of individuals presenting for initial treatment are already daily smokers. Considering these findings and results of trials of tobacco-use treatments in individuals with schizophrenia, clinicians can feel empowered to assess for tobacco use and provide tobacco-use treatments to encourage smoking cessation in individuals with schizophrenia who also smoke.

References

1. Kendler KS, Lonn Larsson S, Sundquist J, Sundquist K. Smoking and schizophrenia in population cohorts of Swedish women and men: a prospective co-relative control study. Am J Psychiatry. 2015;172:1092-1100.

2. Gurillo P, Jauhar S, Murray RM, MacCabe JH. Does tobacco use cause psychosis? Systematic review and meta-analysis. Lancet Psychiatry. 2015;2:718-725.