A new study in The Lancet Psychiatry suggests that smoking tobacco is associated with an increased risk of developing psychosis. Although the association between cigarette smoking and psychosis – particularly schizophrenia – has been acknowledged before, little attention has been directed towards the possibility that cigarettes themselves may increase the risk of psychosis.
Researchers at King’s College London evaluated data from 61 case-controlled and prospective studies (14,555 tobacco users and 273,162 non-users) for trends to estimate the prevalence of smoking in patients presenting with their first episode of psychosis, risk of psychotic illness with daily tobacco use, and age of onset of psychiatric illness based on smoking status.
Of the patients presenting with their first episode of psychosis in this study, 57% were smokers; in case control studies, the patients presenting with their first episode of psychosis were three times more likely to be smokers vs. the control groups, although there was some evidence of publication bias (Egger’s test P=0.018, Begg’s test P=0.007). Daily smokers also developed psychosis approximately a year earlier than non-smokers.
The authors state that this research calls into question the self-medication hypothesis that tobacco use could be used as a means of counteracting negative symptoms of schizophrenia or the side effects of medications for psychosis, but admit that the direction of causality is difficult to determine. In addition, few of the studies reviewed controlled for use of other substances such as cannabis, which may have impacted the findings. Additional research is necessary to provide insight into this potential, but not confirmed, causal relationship; smoking cessation should be encouraged by clinicians for patients in this population.
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