The cytochrome P450 (CYP) gene family strongly influences drug development. We determined potency values for 17,143 compounds against recombinant CYP 1A2, 2C9, 2C19, 2D6, and 3A4 enzymes through an in vitro bioluminescent assay. The compound collections included substances from typical libraries and FDA-approved drugs. Cross-library isozyme inhibition (30–78%) was observed with important differences between collections. While only 7% of the typical screening library was inactive against all five isozymes, 33% of FDA-approved drugs were inactive, reflecting the optimized pharmacological properties of the latter. Unexpectedly, drugs exhibited less activity towards the CYP 2C9 and 2C19 isozymes compared to un-optimized collections. We then identified substructures that differentiated between the five isozymes as well as substructures trending towards active or inactive categories. We describe here a pharmacological compendium to further the understanding of CYP isozymes.