Cocaethylene is a pharmacologically active cocaine metabolite that is formed in the presence of ethanol by the activity of liver enzymes. The pharmacology of cocaethylene has not been extensively investigated and its acute toxicity is unknown. The acute toxicity of cocaethylene was compared to cocaine in Swiss-Webster mice. The LD50 of cocaethylene was 60.7 mg/kg and 63.8 mg/kg in female and male mice, respectively. In comparison, the LD50 of cocaine was 93.0 mg/kg in both female and male mice. These studies demonstrate that the cocaine-alcohol metabolite, cocathylene, is more potent in mediating lethality than the parent drug.