BACKGROUND: Critically ill patients frequently experience alterations in gut microbiota, known as dysbiosis, which has been associated with unfavorable clinical outcomes. The use of probiotics is one approach to modulating gut microbiota. OBJECTIVE: This study aimed to evaluate the effects of probiotic supplementation combined with enteral nutrition (EN) in critically ill patients on infectious, gastrointestinal complications, and clinical outcomes. METHODS: This is a randomized, blinded, placebo-controlled clinical trial conducted with 70 individuals aged ≥18 years, receiving enteral nutrition, and admitted to the emergency intensive care unit (ICU) of a tertiary hospital. The intervention consisted of Lactobacillus paracasei SD 5275, Lactobacillus rhamnosus SD 5675, Lactobacillus acidophilus SD 5221, and Bifidobacterium lactis SD 5674 (10 RESULTS: There was no significant difference in the occurrence of any type of infection or gastrointestinal symptoms between the groups (p ≥ 0.05). The use of antibiotics and laxatives was similar between the groups (p = 1.000 and 0.917, respectively). The average duration of prokinetic use was shorter in the intervention group (2.80 ± 1.52 vs. 6.08 ± 5.58 days, 95 % Confidence interval (CI) -1.39
-0.0594, p = 0.011). Although the number of days on mechanical ventilation, ICU stay, and mortality were lower in the patients who received probiotics, no significant differences were observed between the groups (p ≥ 0.05). CONCLUSION: It is concluded that ICU patients supplemented with probiotics have a shorter duration of prokinetic use. However, supplementation does not directly impact gastrointestinal symptoms, infections, antibiotic use, laxative use, duration of mechanical ventilation, ICU stay, or mortality. REGISTERED AT: Brazilian Clinical Trials Registry (ReBEC) under the number: ID RBR-2kqnj2t. SITE: https://ensaiosclinicos.gov.br/welcome.