The cardiac glycoside poison produced by the upas tree, Antiaris toxicaria, is antiarin.
Antiarin is a cardiac glycoside found in the latex of the upas tree, a species native across parts of tropical Asia. The name covers closely related forms, especially alpha-antiarin and beta-antiarin. Both share the steroid-like aglycone antiarigenin but differ in their attached sugar group, a small structural change that affects their properties.
The latex’s traditional importance came from its use as an arrow, dart, and blowgun poison in island Southeast Asia, including Borneo, the Philippines, Sulawesi, and Malaysia. Concentrated latex was applied to hunting or warfare projectiles. “Upas” therefore refers both to the tree and, in some historical accounts, to the poison prepared from its sap.
As with other cardiac glycosides, antiarin interferes with the sodium-potassium pump in cardiac muscle. That disrupts ion balance and calcium handling: at controlled doses, related compounds can have cardiotonic effects, but excessive doses provoke dangerous contractions, arrhythmias, paralysis, and cardiac arrest. Antiarin is distinct from digitoxin, oleandrin, and cerberin, which come from other poisonous plants.