The age at onset of psychosis and tobacco use: a systematic meta-analysis.

BACKGROUND: There is a well-established but poorly understood association between tobacco use and psychotic illness. The aim of this study was to determine whether tobacco use is associated with an earlier age at onset of psychotic illness. METHODS: Peer-reviewed publications in English reporting the age at onset of psychosis in tobacco-using and non-tobacco-using groups were located using searches of CINAHL, EMBASE, MEDLINE, PsycINFO and ISI Web of Science, and were supplemented by papers located by manual searches and unpublished data obtained by correspondence with primary researchers. A total of 29 samples reported age at onset data in a consecutive series of patients with a diagnosis of schizophrenia related psychosis or first episode psychosis. Information on study design, study population and effect size was extracted independently by three authors. A random effects meta-analysis was performed. RESULTS: There was no significant difference between smokers and non-smokers in age at the onset of psychosis (standardized mean difference = -0.03). CONCLUSION: Unlike cannabis use, tobacco use is not associated with an earlier onset of psychosis.