Delirium in patients with terminal cancer is irreversible and increases treatment resistance, which leads to a deterioration in quality of life.To investigate factors affecting the effectiveness and safety of intravenous chlorpromazine for irreversible delirium in patients with terminal cancer.Multiple regression analysis for factors affecting treatment effectiveness was carried out based on a retrospective comparison between responders and nonresponders to intravenous chlorpromazine.Ninety-seven patients with terminal cancer who were treated with intravenous chlorpromazine for irreversible delirium were included.The rate of patients with ≥50% improvement in mean Nursing Delirium Screening Scale score from pretreatment to day three of chlorpromazine treatment was 0.48 (95% confidence interval [CI]: 0.38-0.58). Factors affecting chlorpromazine treatment effectiveness were hyperactive delirium (odds ratio [OR]: 6.25, 95% CI: 1.14-34.5) and longer survival (OR: 1.096, 95% CI: 1.05-1.14). The mean chlorpromazine dose was low, at 17.9 mg/day. Adverse events were reported in 11 patients (11.3%) by day three of chlorpromazine treatment, and all were observed in patients who survived less than two weeks after chlorpromazine treatment. Patients who died, who had decreased blood pressure during chlorpromazine administration, and who showed acute akathisia all displayed shock index ≥1.Intravenous administration of low-dose chlorpromazine may be an effective and safe treatment option for delirium in patients with terminal cancer who have hyperactive delirium, longer predictive prognosis, and shock index1.