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Cigarette smoking could be a cause of psychosis, not just a means to self-medicate

People who smoke are at increased risk of psychosis, suggests a review of the evidence.

It is well known that people with psychosis are more likely to smoke cigarettes than the general population, but the reasons for this are unclear.

To investigate, researchers conducted a systematic review and meta-analysis of observational studies in which rates of smoking were reported in people with psychotic disorders, compared with controls. Sixty-one studies met the inclusion criteria, with 14,555 tobacco users and 273,162 non-users.

Prevalence of smoking in patients presenting with their first episode of psychosis was 57%. The overall odds ratio for the first episode of psychosis in smokers versus non-smokers was 3.22, although with some evidence of publication bias. The overall relative risk of new psychotic disorders in daily smokers versus non-smokers was 2.18 (95% CI 1.23-3.85). Daily smokers developed illness at a younger age than non-smokers.

The authors suggest that smoking ‘could have a causal role in psychosis’, and is not, as has previously been suggested, simply a means to self-medicate symptoms. One plausible explanation could be the effects of nicotine on the dopamine system, the researchers suggest.

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