Bezoars were sought because they were believed to have the power of a universal antidote against any poison. It was believed that a drinking glass which contained a bezoar would neutralize any poison poured into it. The word "bezoar" comes from the Persianpād-zahr (پادزهر), which literally means "antidote".
The Andalusian physician Ibn Zuhr (d. 1161), known in the West as Avenzoar, is thought to have made the earliest description of bezoar stones as medicinal items. Extensive reference to it is also to be found in the Picatrix, which may be earlier.
In 1575, the surgeon Ambroise Paré described an experiment to test the properties of the bezoar stone. At the time, the bezoar stone was deemed to be able to cure the effects of any poison, but Paré believed this was impossible. It happened that a cook at King's court was caught stealing fine silver cutlery and was sentenced to death by hanging. The cook agreed to be poisoned instead. Ambroise Paré then used the bezoar stone to no great avail, as the cook died in agony seven hours later. Paré had proved that the bezoar stone could not cure all poisons as was commonly believed at the time.
Modern examinations of the properties of bezoars by Gustaf Arrhenius and Andrew A. Benson of the Scripps Institution of Oceanography have shown that they could, when immersed in an arsenic-laced solution, remove the poison. The toxic compounds in arsenic are arsenate and arsenite. Each is acted upon differently, but effectively, by bezoar stones. Arsenate is removed by being exchanged for phosphate in the mineral brushite, a crystalline structure found in the stones. Arsenite is found to bond to sulfur compounds in the protein of degraded hair, which is a key component in bezoars.
A famous case in the common law of England (Chandelor v Lopus, 79 Eng Rep. 3, Cro. Jac. 4, Eng. Ct. Exch. 1603) announced the rule of caveat emptor, "let the buyer beware", if the goods they purchased are not in fact genuine and effective. The case concerned a purchaser who sued for the return of the purchase price of an allegedly fraudulent bezoar. (How the plaintiff discovered the bezoar did not work is not discussed in the report.)
The Merck Manual of Diagnosis and Therapy notes that consumption of unripened persimmons has been identified as causing epidemics of intestinal bezoars, and that up to 90% of bezoars that occur from eating too much of the fruit require surgery for removal.
A 2013 review of 3 databases identified 24 publications presenting 46 patients treated with Coca-Cola for phytobezoars. The cola was administered in doses of 500 mL to up to 3000 mL over 24 hours, orally or by gastric lavage. A total of 91.3% of patients had complete resolution after treatment with Coca-Cola: 50% after a single treatment, others requiring the cola plus endoscopic removal. Surgical removal was resorted to in four patients. 
Types by content
Food boluses (or boli; singular bolus) carry the archaic and positive meaning of bezoar, and are composed of loose aggregates of food items such as seeds, fruit pith, or pits, as well as other types of items such as shellac, bubble gum, soil, and concretions of some medications.
Lactobezoar is a specific type of food bezoar comprising inspissated milk. It is most commonly seen in premature infants receiving formula foods.
Pharmacobezoars (or medication bezoars) are mostly tablets or semiliquid masses of drugs, normally found following overdose of sustained-release medications.
Phytobezoars are composed of indigestible plant material (e.g., cellulose), and are frequently reported in patients with impaired digestion and decreased gastric motility.
Trichobezoar is a bezoar formed from hair – an extreme form of hairball. Humans who frequently consume hair sometimes require these to be removed. The Rapunzel syndrome, a very rare and extreme case, may require surgery.
Types by location
A bezoar in the esophagus is common in young children and in horses. In horses, it is known as choke.
A bezoar in the trachea is called a tracheobezoar.
Production and uses of bezoars
Esophageal bezoars in the nasogastrically fed patients on mechanical ventilation and sedation have been reported to be due to precipitation of certain food types rich in casein, which get precipitated with gastric acid reflux to form esophageal bezoars.
Ox bezoars (cow bezoars) are used in Chinese herbology, where they are called niu-huang (牛黃) or calculus bovis. These are gallstones, or substitutes, from ox or cattle gall bladder bile. There are artificial calculus bovis used as substitutes. These are manufactured from cholic acid derived from bovine bile. In some products, they claim to remove "toxins" from the body.
In alchemy, "animal bezoar" is the heart and lungs of the viper, pulverized together. Mineral bezoar is an emetic powder of antimony, correct with nitric acid, and softened by repeated lotions, which were said to carry off the purgative virtue of the antimony, and substitute a diaphoretic one. It promoted sweat like the stone of the same name.
^Buckley NA, Dawson AH, Reith DA (January 1995). "Controlled release drugs in overdose. Clinical considerations". Drug Safety: an International Journal of Medical Toxicology and Drug Experience12 (1): 73–84. doi:10.2165/00002018-199512010-00006. PMID7741985.
^Kishan, Asn; Kadli, NK (2001). "Bezoars". Bombay Hospital Journal.
Martín-Gil FJ, Blanco-Ávarez JI, Barrio-Arredondo MT, Ramos-Sanchez MC, Martin-Gil J. Jejunal bezoar caused by a piece of apple peel – Presse Med, 1995 Feb. 11; 24(6):326.
The Poison Sleuths: Arsenic – The King of Poisons. Retrieved March 10, 2007. (This webpage is a reprint by the author of an article originally published in the 1997 issue of Science Reporter, published by the National Institute of Science Communication (CSIR) in India.)
Borschberg, Peter, "The Euro-Asian Trade in Bezoar Stones (approx. 1500–1700)", Artistic and Cultural Exchanges between Europe and Asia, 1400–1900: Rethinking Markets, Workshops and Collections, ed. Thomas DaCosta Kaufmann and Michael North, Aldershot: Ashgate, 2010, pp. 29–43.
Borschberg, Peter, "The Trade, Forgery and Medicinal Use of Porcupine Bezoars in the Early Modern Period (c.1500–1750)", ed. Carla Alferes Pinto, Oriente, vol. 14, Lisbon: Fundação Oriente, 2006.