A cardiac glycoside poison found in hellebore plants, affecting heart function.
From 'hellebore' plus the chemical suffix '-in.' Named in the 19th century when chemists isolated this specific cardiac toxin from hellebore extracts.
Helleborin is so poisonous it stops your heart, yet medieval doctors gave it to mad people—they were essentially playing cardiac roulette, and the fact that some patients got better suggests the 'shock' itself might have been therapeutic!
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