Chlorpromazine (3, 10, 20, 40, and 60 μM) decreases the peak currents of hNav1.7 in a concentration-dependent manner, with IC50 of 25.9 μM with a Hill coefficient of 2.3. Chlorpromazine (25 μM) produces strong use-dependent inhibition of the hNav1.7 current. Chlorpromazine blocks the hNav1.7 channel, independent of calmodulin. Chlorpromazine blocks HERG potassium channels with an IC50 value of 21.6 μM and a Hill coefficient of 1.11. Chlorpromazine (1, 10, 100 μM) blocks HERG potassium channels expressed in Xenopus laevis oocytes in a concentration-dependent manner. Chlorpromazine blocks HERG potassium channels in the activated state.