Here, we showed that eight bipolar drugs (aripiprazole, fluphenazine, thioridazine, pimozide, trifluoperazine, quetiapine, loxapine, and iloperidone) that are FDA-approved repositioning drugs exhibited sensitization effects at low doses in P-gp overexpressed drug-resistant cancer cells (Table 1). This evidence concerns the gene PGP and cancer.