Objective: To test the compatibility of intravenous (IV) lactated Ringer’s injection (LR) with 94 injectable (IV) drugs during simulated Y-site administration. Methods: Ninety-four IV drugs were investigated for compatibility with LR (Baxter). Each sample was prepared in duplicate and performed at room temperature. Two observers performed visual evaluation independently immediately upon mixing and then 15 minutes, 1 hour, 2 hours, 3 hours, and 4 hours after admixture. Another observer performed a particle counting test on 1 of the 2 duplicates of each admixture that did not immediately show incompatibility and then after 4 hours by a light obscuration particle count test. Results: Of the 94 tested drugs, 86 were found to be compatible with LR. A total of 8 drugs were found to be physically incompatible. Of these incompatible drugs, 7 were directly identified visually and 1 was confirmed by the light obscuration particle count test. Conclusion: Lactated Ringer’s injection was physically compatible for 4 hours with 86 tested drugs during simulated Y-site administration. Eight drugs, ciprofloxacin, cyclosporine, diazepam, ketamine, lorazepam, nitroglycerin, phenytoin, and propofol, were found to be incompatible and should not be administered with LR.