Saxitoxin is an alkaloid isolated from the marine dinoflagellates and cyanobacteria that causes paralytic shellfish poisoning. It has a role as a neurotoxin, a toxin, a sodium channel blocker, a marine metabolite and a cyanotoxin. It is a carbamate ester, a member of guanidines, an alkaloid, a pyrrolopurine, a ketone hydrate and a paralytic shellfish toxin. It is a conjugate base of a saxitoxin(2+).