Tetrodotoxin (anhydrotetrodotoxin 4-epitetrodotoxin, tetrodonic acid, TTX) is a potent neurotoxin with no known antidote. Tetrodotoxin blocks action potentials in nerves by binding to the pores of the voltage-gated, fast sodium channels in nerve cell membranes.^[1] The binding site of this toxin is located at the pore opening of the voltage-gated Na⁺ channel. Its name derives from Tetraodontiformes, the name of the order that includes the pufferfish, porcupinefish, ocean sunfish or mola, and triggerfish, several species of which carry the toxin. Although tetrodotoxin was discovered in these fish and found in several other animals (e.g., Blue-ringed Octopus, Rough-skinned newt,^[2] and Naticidae^[3]) it is actually the product of certain bacteria such as Pseudoalteromonas tetraodonis, certain species of Pseudomonas and Vibrio, as well as some others.

Its mechanism was discovered in the early 1960s by Toshio Narahashi working at Duke University.