CH 223191 is a specific and potent antagonist to the aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor that is involved in drug and xenobiotic metabolism. Unlike other AhR antagonists, it does not react with the estrogen receptor and is observed to effect AhR-dependent reporter gene expression in human, mouse, rat, and guinea pig cell lines. CH223191 is reported to exhibit AHR-independent pro-proliferative properties.