We extracted from the ChEMBL31 database a set of molecules tested against COX-2. A total of 12,155 entries in the ChEMBL31 database had data related to COX-2, from which only 7,342 had unique ChEMBL Molecule IDs, and 7,310 had unique SMILES strings, as some same molecules are used in various experiments. For example, Celecoxib (CHEMBL118) is present in 264 entries, with 188 different measurements of IC50s, 63 measures of "inhibition" (reported as percent inhibition with respect to some chosen reference), seven measurements of "activity" measurements (reported just as active or not active) and six entries for other kinds. As it is the most reported value, we considered only molecules with reported IC50s. In cases where multiple values are reported for the same molecule, we used the mode of the distribution as the value for that molecule's IC50. After filtering the database for unique molecules with valid IC50 data and removing molecules with atoms other than C, N, O, H, S, P, As, Se, or X (X=halogen), we were left with 3,590 unique molecules. We refer to this dataset as the "ChEMBL31-IC50s" dataset.