Background–Hepatic encephalopathy(HE) in acute-on-chronic liver failure(ACLF) is associated with significant morbidity and mortality. We conducted a prospective, randomized controlled clinical trial to study efficacy of intravenous branched chain amino acids(IV-BCAA) with lactulose versus lactulose alone for improvement in HE at 24h, day 3 & day 7. Primary outcome was improvement in encephalopathy by ≥ 1 grade at 72 hours.Patients and Methods–EASL defined ACLF patients with overt HE were assessed and randomized into experimental arm (IV-BCAA - 500mL/day for 3 days + Lactulose; n=39) and comparator arm (Lactulose alone; n=37). Six patients developed COVID-19 after randomization & were excluded (4-experimental arm & 2-comparator arm).Results–Of 222 screened patients, 70 (35 in each arm) were included in analysis. Baseline characteristics including HE grade (2.9 ± 0.7 vs 2.8 ± 0.7;P = 0.86) and CLIF-C ACLF score (54.2 ± 5.6 vs 54.8 ± 5.7;P = 0.65) were similar. Overall survival was 40% at 28 days (48.5% vs 31.4%;P=0.14). Improvement in HESA by ≥1 grade at 24h occurred in 14 patients (40%) in BCAA arm and 6 patients (17.1%) in control group (P=0.03) which translated to shorter ICU stay. Median change in HESA at 24h was more in BCAA arm than control arm(P=0.006) which was not sustained at day 3 or 7. Ammonia levels did not correlate with grade of HE (Spearman’s correlation coefficient(ρ) = - 0.0843;P=0.29).ConclusionIntravenous BCAA does not lead to a sustained improvement in HE grade in ACLF.Trial registration noNCT04238416 (clinicaltrials.gov)