M8-B is an antagonist of transient receptor potential melastatin 8 (TRPM8) that blocks activation by cold, icilin , or menthol in vitro (ICs = 7.8, 26.9, and 64.3 nM, respectively). It displays no effect at other TRP channels. M8-B decreases deep body temperature in wild-type mice and rats but has no effect on body temperature in TRPM8 KO mice.