IDO1/TDO-IN-4 is a potent IDO1/TDO dual inhibitor, with IC50 values of 3.53 μM (IDO1) and 1.15 μM (TDO). IDO1/TDO-IN-4 forms hydrogen bond with IDO1, and π−π stacking interaction with TDO. IDO1/TDO-IN-4 can be used in the research of depression, and depression-induced infectious, metabolic, and autoimmune disorders[1].