Objective: Antibiotic time-outs (ATOs) have been advocated to improve antibiotic use without dedicated stewardship resources, but their utility is poorly defined. We sought to evaluate the effectiveness of an ATO led by a team-based pharmacist. Design: Cluster randomized controlled trial. Setting: Six medicine teams at an academic medical facility. Patients: Inpatients who received antibiotics and were cared for by a medicine team. Intervention: In phase A (2 months) pharmacist-led ATOs were implemented on 3 medicine teams (ATO-A) while 3 teams maintained usual care (UC-A). In phase B (2 months), ATOs were continued in the ATO group (ATO-B) and ATOs were initiated in the UC group (UC ATO-B). We targeted 2 ATO points: early (<72 hours after antibiotics were initiated) and late (after the early period but ≤5 days after antibiotic initiation). Results: In total, 290 ATOs were documented (181 early, 87 late, and 22 subsequent) among 538 admissions. The most common ATO recommendations were narrow therapy (148 of 290), no change (124 of 290), and change to oral (30 of 290). ATO initiation was lower in the UC ATO-B group than in either ATO group (21.8% UC ATO-B vs 69.2% ATO-A and -B). Overall antibiotic use was not different between the groups (P = .51), although intravenous (IV) levofloxacin use decreased in the UC group after ATO implementation (49 DOT/1,000 PD vs 20 DOT/1,000 PD; P = .022). The ratio of oral (PO) to intravenous (IV) DOT was lower in the UC group than in any of the ATO groups (P = .032). We detected no differences in mortality, length of stay, readmission, C. difficile infection, or antibiotic adverse events. Conclusions: Implementation of a pharmacist-led ATO was feasible and well accepted but did not change overall antibiotic use. An ATO may promote increased use of oral antibiotics, but more effective strategies for self-stewardship are needed.