PurposeThe differential effect of fentanyl vs. morphine analgosedation on the development of hospital inpatient delirium in patients receiving mechanical ventilation is unknown. We aimed to compare the incidence of coding for delirium and antipsychotic medication use in patients treated with fentanyl vs. morphine in the ANALGESIC trial. Materials and methodsWe obtained data from a cluster randomized, cluster crossover trial of fentanyl vs. morphine for analgosedation on antipsychotic use and coding diagnosis of delirium and compared these outcomes according to treatment allocation. We assessed the relationship between opioid choice and dose, hospital inpatient delirium, and outcomes. ResultsAmong 681 patients enrolled in the ANALGESIC trial, 160/344 (46.5%) in the fentanyl group vs. 132/337 (39.1%) in the morphine group (absolute difference 7.34% [95% CI -0.9 to 14.78]; RR: 1.19 [95%CI 1.00 to 1.41]; p = 0.053) developed hospital inpatient delirium. Antipsychotic use was linearly related to opioid dose. Antipsychotic use was not associated with increased mortality. ConclusionsFentanyl is associated with a higher incidence of hospital inpatient delirium when used for analgosedation compared with morphine, and the dose of opioid is linearly related to the need for antipsychotic medication administration. The role of analgosedation in promoting delirium requires further investigation.