Smoking may worsen depressive symptoms and quality of life in patients with psychosis, according to results from a prospective cohort study published in The Lancet Psychiatry.

Investigators sought to test the “self-medication hypothesis,” which postulates that the high prevalence of smoking in patients with psychosis may be explained by the ameliorating effect of smoking on symptoms. The study cohort comprised patients with a non-affective psychosis (n=1094), unaffected siblings (n=1047), and healthy controls (n=579). Adult patients with non-affective psychosis were recruited by clinicians in The Netherlands and Belgium between January 2004 and March 2014. Smoking status and number of cigarettes per day were assessed at baseline and at 3-year and 6-year follow-up visits by means of the Composite International Diagnostic Interview. Symptom frequency and severity were self-rated using the Community Assessment of Psychotic Experience. Quality of life was captured using the World Health Organization Quality of Life schedule. Multiple linear mixed-effects regression analyses were performed to adjust for confounders.

At baseline, 729 (67%) patients with psychosis reported smoking, compared with just 401 (38%) siblings and 145 (25%) healthy controls. The mean (standard deviation) number of cigarettes per day was 17.5 in patients with psychosis. Linear mixed-effects analyses indicated that smoking in patients and siblings was associated with more frequent positive symptoms (P <.0001 for patients; P =.0019 for siblings), negative symptoms (P <.0001 for both), and depressive symptoms (P <.0001 for both). Smoking was also associated with lower quality of life in patients with psychosis (P <.0001) and siblings (P =.0002). In controls, smoking was associated with greater frequency of subclinical positive symptoms (P =.0016) and depressive symptoms (P =.0432) compared with controls who did not smoke. In addition, patients who began smoking during follow-up experienced a significant increase in self-reported positive symptoms (P =.0381). By contrast, smoking cessation during follow-up was not associated with any change in subclinical symptoms or quality of life. However, a negative association between number of cigarettes per day and quality of life was observed among patients.

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These data challenge the self-medication hypothesis, instead suggesting that smoking may worsen psychiatric symptoms in patients with psychosis and increase the risk for subclinical symptoms in controls.

“The absence of long-term symptomatic relief from smoking should encourage clinicians to help patients with psychosis to quit smoking,” state the study authors.

Reference

Vermeulen J, Schirmbeck F, Blankers M, et al. Smoking, symptoms, and quality of life in patients with psychosis, siblings, and healthy controls: a prospective, longitudinal cohort study. Lancet Psychiatry. 2019; 6(1):25-34.