Cohen, Hannah RHannah RCohenCHIN-KUO CHANGAhn-Robbins, DeborahDeborahAhn-RobbinsBogdanowicz, KarolinaKarolinaBogdanowiczChandran, DavidDavidChandranKartoglu, EmreEmreKartogluShetty, HiteshHiteshShettyVermeulen, Jentien MJentien MVermeulenSanyal, JyotiJyotiSanyalStewart, RobertRobertStewartSchirmbeck, FrederikeFrederikeSchirmbeckde Haan, LieuweLieuwede HaanHayes, Richard DRichard DHayes2026-03-232026-03-232026-02-16https://scholars.lib.ntu.edu.tw/handle/123456789/736563Background: Comorbid obsessive-compulsive disorder (OCD) or obsessive-compulsive symptoms (OCS) are common in people with severe mental illness (SMI; including schizophrenia, bipolar disorder and schizoaffective disorder), with little known about associations with smoking. Aims: To estimate the association between OCD/OCS and smoking status among people with SMI in a huge electronic database. Method: Using the Clinical Records Interactive Search (CRIS) platform for data of service users in the South London and Maudsley (SLaM) NHS Foundation Trust, tobacco smoking status was retrospectively detected through an algorithm of natural language processing technique, categorising into 'current smoker', 'ex-smoker' and 'non-smoker' by the clinical notes of SMI individuals during 2007-2015. A hierarchical assignment rule was applied following the order of 'smoker', 'ex-smoker' and then 'non-smoker' in an individual. Logistic regression was used to examine the association between smoking and OCS in people with SMI for univariable and multivariable analyses. Results: We identified 15 479 SMI individuals (56% male; mean age 41 years old), with 90.4% ever smoked. Among them, 2320 (15%) had OCS (without OCD), while 2174 (14%) had a clinical diagnosis of comorbid OCD. After adjusting for demographics and functional status as confounders, both SMI individuals with OCS only and an OCD diagnosis were significantly more likely to have ever smoked (adj. odds ratio 1.47, 95% CI 1.23, 1.76 and adj. odds ratio 1.33, 95% CI 1.11, 1.60, respectively) compared with those without OCD/OCS. Conclusions: In this large-scale analysis of people with SMI, we found that individuals with OCS or OCD were more likely to have ever smoked.enObsessive–compulsive symptomnatural language processingobsessive–compulsive disordersevere mental illnesssmokingjournal article10.1192/bjo.2025.1096541693111