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Daily tobacco use may increase risk for psychosis, earlier age at psychosis onset

Daily tobacco use may increase risk for psychosis and an earlier age at onset of psychotic illness, according to study findings in Lancet Psychiatry.

“Although the association between smoking tobacco and psychosis (in particular, schizophrenia) has been acknowledged, the reasons why people with psychosis are more likely to smoke compared with the rest of the population are still unclear,” study researcher Pedro Gurillo, MD, of Torrevieja’s Hospital in Alicante, Spain, and colleagues wrote. “Several theories have been proposed, many focusing on the idea of self-medication — ie, smoking corrects a pharmacological abnormality (such as excessive dopamine blockade induced by antipsychotics), counteracts negative or cognitive symptoms of schizophrenia, or relieves boredom or distress. Little attention has been directed towards the possibility that cigarette smoking might increase risk for the disorder.”

Researchers conducted a systematic review and meta-analysis of 61 studies comprising a sample of 14,555 tobacco users and 273,162 nonusers to determine if daily tobacco use affected risk for psychotic illness, earlier age at onset of psychotic illness or if earlier age at initiation of smoking increased risk for psychosis.

Patients who presented with their first episode of psychosis had a smoking prevalence of 0.57 (95% CI, 0.52-0.61; P < .0001).

Compared with nonsmokers, smokers had an overall odds ratio of 3.22 (95% CI, 1.63-6.33) for first psychotic episode, according to analysis of case-control studies.

In prospective studies, daily smokers had an overall risk of 2.18 (95% CI, 1.23-3.85) for new psychotic disorders compared with nonsmokers.

Daily smokers developed psychotic disorders at an earlier age than non-smokers, with a weighted mean difference of –1.04 years (95% CI, –1.82 to –0.26).

Individuals with psychosis started smoking at an earlier age than healthy controls.

“Large, longitudinal, prospective studies are needed to investigate the relations between smoking tobacco and cannabis and development of anxiety, depression, and psychotic disorders, adjusting for the effects of other substances, to enable more stringent examination of whether cigarette smoking has a causal role in the development of psychosis. Such studies will allow us to assess the public health importance of the results presented here,” Helen L. Alderson, PhD, and Stephen M. Lawrie, MBChB, MRCPsych, MPhil, MD, FRCPsych, of the University of Edinburgh, wrote in an accompanying editorial. “To say that smoking causes psychosis would be premature, but the time might not be too much longer before cigarette smoking is recognized as a risk factor for psychosis as well as anxiety and depression.” – by Amanda Oldt

Disclosure: Gurillo and colleagues report no relevant financial disclosures. Alderson reports no relevant financial disclosures. Lawrie reports personal fees from Janssen and Sunovion, grants and personal fees from Roche, and grants from Pfizer and Abbvie, outside the submitted work.