The screening of a commercially available library of compounds has proved a successful strategy for the identification of a lead compound in a drug discovery programme. Here, we analysed 880 off-patent drugs, which initially comprised the Prestwick Chemical library, as sources of bacterial endotoxin neutralizers. We identified 3,3',5-triiodo-thyroacetic acid (tiratricol) as a non-antibacterial compound that neutralizes the toxic lipopolysaccharide.