In vitro stereoselective inhibition of ginsenosides toward UDP-glucuronosyltransferase (UGT) isoforms.

•Stereoselective inhibition of ginsenoside C-20 isomers on the UGTs has not been fully characterized.•Stereoselective inhibitions were observed with different potencies on the ten UGTs.•Of the tested twelve ginsenosides isomers, 20(R)-Rg3 had the strongest inhibition on the UGT1A8.•20(S)-Rg3, 20(S)-Rh2, 20(R)- and 20(S)-PPT also weakly inhibited UGT1A8.•There may be a potential for herb-drug interactions between processed ginseng and UGT1A8 substrates.