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.