Menthofuran- 13 C 2 is 13 C labeled Menthol. Menthol is an analgesic and TRPM8 modulator. TRPM8 is a cold temperature sensing ion channel, and Menthol can regulate TRPM8 to exert analgesic and anti-irritation mechanisms. Menthol stimulates cold receptors and produces a cooling sensation by inhibiting Ca ++ currents in neuronal cell membranes. Menthol also improves oral nicotine rejection in mice.