Results61 studies comprising 72 samples were analysed (figure 1; appendix pp 1–2). 7475 people with psychosis were smokers (mean 33•2 per sample [SD 195•7]) and 5670 people with psychosis were non-smokers (mean 20•7 per sample [SD 148•1]). Figure 2 shows the prevalence of smoking in people presenting with their first episode of psychosis. 34 samples were analysed, from 34 studies (appendix p 3).11,15,19–23,29,31–33,35–39,46,49–65 In the total sample of smokers, prevalence of smoking in peoplepresenting with their first episode of psychosis was 0∙57 (95% CI 0∙52–0∙62; p<0∙0001). Between-sampleheterogeneity was significant, with an I² of 88•0%. All definitions of smoking (including daily smoking)were included in our analysis of smoking prevalence in people presenting with their first episode of psychosis. 12 samples were obtained for the analysis, from 11 case control studies.15,21–23,32,34–39 Compared with controls, the overall prevalence of smoking in people presenting with their first episode of psychosis was three times higher (odds ratio 3∙22, 95% CI 1•63–6∙33; p=0∙001; figure 3).Between-sample heterogeneity was significant, with an I² of 82•1%. Findings of Begg’s test (p=0∙007) and Egger’s test (p=0∙018) suggested that publication bias might have been present. In the analysis of daily smoking status, four samples were identified, from three studies,15,21,32 with an overall odds ratio of 1∙01 (95% CI 0∙58–1∙76; p=0∙976; figure 3). Between-sample hetero geneity was significant,with an I² of 53•3%. In our analysis of daily tobacco use and risk of psychotic disorder, five longitudinal prospective studies were identified of six samples from the general population (all samples measured risk of schizophrenia).18–20,46,66 Compared with non-smokers, the incidence of new psychotic disorders in daily smokers was higher (overall risk ratio 2∙18, 95% CI 1∙23–3•85; p=0∙007; fi gure 4). Between sampleheterogeneity was significant, with an I² of 97•7%. Some evidence was recorded that publication biascontributed to the findings, supported by Egger’s test (p=0∙002) and Begg’s test (p=0∙024). We also identified one study comprising a cohort of prodromal individuals,33 in which the risk ratio of developing new-onset psychotic illness in daily smokers versus non-smokers was 7∙00 (95% CI 2∙35–20∙83). In our analysis of daily tobacco use and age at onset of psychosis compared with non-smokers, 26 samples wereincluded, from 23 studies.13,19,25–28,30,40–43,46,53,59,61,67–74 Daily smokers developed psychotic illness at an earlier age, compared with non-smokers (24∙25 years vs 25∙63 years; weighted mean difference –1∙04, 95% CI –1∙82 to –0∙26; p=0∙009; figure 5). Between-sample heterogeneity was significant, with an I² of 66•3%. No evidence was recorded that publication bias contributed to the findings, as shown by Egger’s test (p=0∙149) and Begg’s test (p=0∙103). When the analysis was divided according to the study country,75 a significant difference was noted between group means (one-way ANOVA F=4∙32;p=0∙049). Our analysis was based on data showing differences in the age at initiation of smoking in
countries in Europe, North America, and Australasia (eg, Australia, Finland, Spain, Sweden, and the USA) versus countries in Asia and the Middle East (eg, Egypt, Japan, and Turkey); specifically, women in Asian countries were seen to begin smoking at a later age. In Europe, North America, and Australasia, 18 samples from 16 studies were analysed,13,19,25,26,28,40–43,46,53,59,61,67,68,70 with a weighted
mean difference of –1∙56 (95% CI –2•52 to –0∙59; p=0∙002; figure 5). In Asia and the Middle East, eight
samples from seven studies were analysed,27,30,69,71–74 with a weighted mean difference of 0∙24 (–0∙56 to 1∙04; p=0∙554). No between-sample heterogeneity was recorded, with an I² of 0%. In the analysis of age at initiation of smoking in people with psychosis compared with controls, 15 samples were
identified from 12 studies.12,14,19,24,26,31,32,43–45,53,76 Age at initiation of smoking cigarettes did not differ between patients with psychosis and controls, with a weighted mean difference
of –0•44 (95% CI –1•21 to 0∙34; p=0∙270; figure 6). Between-sample hetero geneity was significant, with an I² of 81•0%. No evidence was recorded that publication bias contributed to the findings, supported by Egger’s test (p=0∙957) and Begg’s test (p>0∙99).
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