Figure 2 showed the cell viability of these cells treated with three different chemical substrates with and without 1 μM or 3 μM tetrandrine, and their IC50 values were compared. Based on the cytotoxicity assay mentioned above, 1 μM and 3 μM were considered as non-toxic concentrations of tetrandrine (Figure 1). Our data showed that tetrandrine significantly enhanced the sensitivity of chemical drugs in drug resistant cancer cell lines SW620/Ad300, KB-C2, and HEK293/ABCB1 that overexpressed ABCB1 in a dose-dependence manner (Figure 3, Table 2). Here, ABCB1 is linked to cancer.