Objectives: Constipation, a clinical manifestation of gastrointestinal hypomotility, is a common and potentially serious complication of clozapine therapy, requiring laxatives for its prevention and treatment. We explored the predictive factors of the increased laxative use in inpatients receiving a long-term clozapine therapy. Methods: In the cross-sectional study of 93 patients in a psychiatric rehabilitation hospital, we examined a four-week prevalence of laxative use and a range of demographic and clinical factors associated with the number of prescribed laxatives. Results: Seventy-four percent of inpatients with schizophrenia were prescribed laxatives, and they were statistically significant older and taking higher daily doses of clozapine. In generalized Poisson regression analysis, the clozapine dose, age, and comorbid diabetes mellitus and hypothyroidism were independently associated with the number of concurrently used laxatives. No association was found between the laxatives and gender, duration of clozapine treatment, and the number of other medications with a potential to cause constipation. Conclusion: The clozapine dose, age, diabetes mellitus, and hypothyroidism were shown to be the independent predictors of the increased laxative use among inpatients on clozapine and might be associated with the increased risk of clozapine-induced constipation and gastrointestinal hypomotility.