Well, it's not that it's poisonous per se just that it has coumarin in it, which is an anticoagulant. In the US, the levels of coumarin found in ?ubrówka are deemed too high, so genuine ?ubrówka is illegal. I believe there are some brands that have had the coumarin removed, but I suspect that they don't taste as nice. From http://www.polishvodka.com.pl/fr_zubrowka.htm: "Bison grass contains coumarin, a glycoside with a distinctive fragrance, once generally used to flavor tobacco, cakes and beverages. Today, because coumarin has been found to have anticoagulant properties, it is allowed only in tiny amounts which the Polish health authorities deem harmless. ?ubrówka contains only about a dozen milligrams of coumarin per liter, derived from an infusion of one or two kilos of bison grass per thousand liters of vodka."