We investigated the effect of mexiletine on the formalin-induced nociceptive response and its modulation by diabetes. We also investigated the effects of mexiletine on intrathecally-administered substance P- and somatostatin-induced nociceptive responses in both non-diabetic and diabetic mice. Intraperitoneal injection of mexiletine (30 mg/kg) significantly reduced the duration of the formalin-induced nociceptive response in both non-diabetic and diabetic mice. When mexiletine (30 mg/kg, i.p.) was injected 30 min before injection of substance P (SP), it significantly inhibited SP-induced nociceptive responses in both non-diabetic and diabetic mice. Furthermore, mexiletine also significantly inhibited the intensity of somatostatin (SST)-induced antinociceptive effect of mexiletine in diabetic mice involves the inhibition of SP- and SST-mediated nociceptive transmission in the spinal cord.