Oenanthotoxin is a toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

 extracted from hemlock water dropwort (Oenanthe crocata) and other plants of the genus Oenanthe

Water dropwort

The water dropworts, Oenanthe , are a genus of plants in the family Apiaceae. Most of the species grow in damp ground, in marshes or in water....

. It is a central nervous system poison, and acts as a noncompetitive gamma-aminobutyric acid

Gamma-aminobutyric acid

γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...

 antagonist. This toxin played some role in euthanasia in ancient Sardinia, for inducing risus. It was first isolated by a Boehm scientist in 1876 and was crystallized in 1949 by E.G.C. Clarke, D.E. Kidder and W.D. Robertson (J. Pharm. Pharmacol.). It is structurally closely related to the toxins cicutoxin

Cicutoxin

Cicutoxin is a poisonous polyyne and alcohol found in various plants, most notably water hemlock . It is structurally related to the oenanthotoxin of hemlock water dropwort....

 and carotatoxin

Carotatoxin

Carotatoxin is a poisonous polyyne and alcohol found in carrot . It is structurally related to the oenanthotoxin and cicutoxin. It occurs approximately in a concentration of 2 mg/kg....

.