Metabolic inhibitors and receptor antagonists are indispensable tools for the molecular life scientist. By blocking specific enzymes or receptor-mediated signal transduction cascades, they simplify the analysis of complex cellular processes especially when it is essential to demonstrate that a process of interest is functionally linked to a particular enzyme or receptor. From antibiotics to statins, modern medicine relies on the reliability and ease-of-use of enzyme- and receptor-directed inhibitors and antagonists.The Inhibitor Index is a comprehensive, curated compendium of over 7,800 enzyme inhibitors and receptor antagonists, including many toxins, poisons, and metabolic uncouplers.