A bezoar stone (/ˈbizɔːr/ BEE-zor) is a mass often found trapped in the gastrointestinal system,[2] though it can occur in other locations.

Ox bezoars (niu-huang (牛黃) or calculi bovis) are used in Chinese herbology[vague] to treat various diseases.

In 1567, French surgeon Ambroise Paré did not believe that it was possible for the bezoar to cure the effects of any poison and described an experiment to test the properties of the stone.

The toxic compounds in arsenic are arsenate and arsenite; each is acted upon differently by the bezoars: arsenate is removed by being exchanged for phosphate in brushite found in the stones, while arsenite is bound to sulfur compounds in the protein of degraded hair, which is a key component in bezoars.

1603) announced the rule of caveat emptor ("let the buyer beware") if the goods purchased are not in fact genuine and effective.

Bezoars were important objects in cabinets of curiosity and in natural-history collections, mainly for their use in early-modern pharmacy and in the study of animal health.