A neurotoxin is a toxin that acts specifically on nerve cells – neurons – usually by interacting with membrane proteins and ion channels.

Many of the venoms and other toxins that organisms use in defense against vertebrates are neurotoxins. A common effect is paralysis, which sets in extremely rapidly. The venom of bees, scorpions, pufferfish, spiders and snakes can contain many different toxins. Many neurotoxins act by affecting voltage-dependent ion channels.