Both insomnia and positive symptoms are linked to suicidal ideation (SI) in schizophrenia, yet their interaction remains unexplored. This study aims to investigate whether insomnia moderates the relationship between positive symptoms and SI in a large sample of Chinese patients with chronic schizophrenia.

We recruited 1407 patients and assessed them using the Positive and Negative Syndrome Scale (PANSS), Insomnia Severity Index (ISI), and Beck Scale for Suicide Ideation (BSSI). We also collected demographic information and lifetime history of suicide attempts (SA). Positive symptoms were evaluated using the PANSS positive factor. Multivariate logistic regression and moderation analysis were performed.

The prevalence of insomnia and SI was 13.5 % and 9.7 %, respectively. ISI scores (adjusted odds ratio [AOR]: 1.06; 95 % confidence interval [CI]: 1.01–1.10, p = 0.011), PANSS positive factor (AOR: 1.05; 95 % CI: 1.01–1.09, p = 0.008), PANSS mood factor (AOR: 1.16; 95 % CI: 1.10–1.22, p < 0.001), and lifetime SA (AOR: 4.35; 95 % CI: 2.86–6.61, p < 0.001) were independently associated with SI. Moderation analysis revealed that insomnia amplified the association between positive symptoms and SI. Specifically, higher levels of insomnia significantly strengthened this relationship (b = 0.086, 95 % CI = 0.048–0.124, p < 0.001), while the association was negligible in patients with low levels of insomnia (b = −0.003, 95 % CI = -0.042–0.036, p = 0.870).

Both insomnia and positive symptoms were independently related to SI in schizophrenia, with insomnia moderating the relationship between positive symptoms and SI. Further studies are needed to test whether interventions against insomnia and positive symptoms would be effective at reducing SI in this population.