The decomposition induced by enzymes may occur in two ways. Maltase partially decomposes it, giving d-glucose and mandelic nitrile glucoside, C6H5CH(CN)O·C6H11O5; this compound is isomeric with sambunigrin, a glucoside found by E.E. Bourquelot and Danjou in the berries of the common elder, Sambucus nigra. Emulsin, on the other hand, decomposes it into benzaldehyde, cyanide, and two molecules of glucose; this enzyme occurs in the bitter almond, and consequently the seeds invariably contain free cyanide and benzaldehyde. An "amorphous amygdalin" is said to occur in the cherry-laurel. Closely related to these glucosides is dhurrin, C14H17O7N, isolated by W. Dunstan and T. A. Henry from the common sorghum or "great millet," Sorghum vulgare; this substance is decomposed by emulsin or hydrochloric acid into d-glucose, cyanide, and 4-hydroxybenzaldehyde.
Amygdalin is sometimes confounded with laevomandelonitrile, also called laetrile for short; however, amygdalin and laetrile are different chemical compounds. Laetrile, which was patented in the United States, is a semi-synthetic molecule sharing part of the amygdalin structure, while the "laetrile" made in Mexico is usually amygdalin, the natural product obtained from crushed apricot pits, or neoamygdalin.
Though it is sometimes sold as "Vitamin B17", it meets none of the criteria of a vitamin. Amygdalin/laetrile was claimed to be a vitamin by Ernst Krebs, Jr in the hope that if classified as a nutritional supplement it would escape the federal legislation regarding the marketing of drugs. He could also capitalise on the public fad for vitamins at that time.
A 2006 Cochrane review of the evidence concluded that there is no sound evidence that laetrile is an effective cancer treatment and that there is considerable doubt about its safety. It has not been approved for this use by the United States' Food and Drug Administration. The U.S. government's National Institutes of Health evaluated the evidence, including case reports and a clinical trial, and concluded that they showed little effect. A 1982 trial of 178 patients found that tumor size had increased in all patients. Minimal side effects were seen except in two patients who consumed bitter almonds and suffered from cyanide poisoning.
In 1974, the American Cancer Society officially labelled laetrile as quackery, but advocates for laetrile dispute this label, asserting that financial motivations have tainted the published research. Some North American cancer patients have travelled to Mexico for treatment with the substance, allegedly under the auspices of Dr. Ernesto Contreras. One of these patients was actor Steve McQueen, who died in Mexico following surgery to remove a stomach tumour while undergoing treatment for mesothelioma. Laetrile advocates within the United States include the late Dean Burk Ph.D., a former chief chemist of the National Cancer Institute's cytochemistry laboratory and national arm wrestling champion Jason Vale, who claimed that his kidney, pancreatic and spleen cancer were cured by eating apricot seeds. Vale was convicted in 2003 for, among other things, marketing laetrile; the US Food and Drug Administration continues to seek jail sentences for vendors selling laetrile for cancer treatment, calling it a "highly toxic product that has not shown any effect on treating cancer."
Amygdalin was first isolated in 1830. In 1845 it was used for cancer in Russia, and again in the 1920s in the United States, but it was considered too poisonous. In the 1950s a reportedly nontoxic, synthetic form was patented for use as a meat preservative, and later marketed as Laetrile for cancer treatment. In 1972, Memorial Sloan-Kettering Cancer Center board member Benno Schmidt convinced the hospital to test laetrile so that he could assure others of its ineffectiveness "with some conviction". However, the respected scientist put in charge of the testing, Kanematsu Sugiura, found that laetrile inhibited the secondary tumors in mice without destroying the primary tumors. He repeated the experiment three times with the same results, and then three more times. In a blinded test, however, he was unable to conclude that laetrile had anticancer activity. His first three experiments were not published because, in the words of Chester Stock, Sugiura's supervisor, "it would have caused all kind of havoc". Nevertheless the results were leaked in 1973, causing a stir. Subsequently laetrile was tested on 14 tumor systems, and a Sloan-Kettering press release concluded that "laetrile showed no beneficial effects". Three other researchers were unable to confirm Sugiura's results, although one of three did confirm Sugiara's results in one of his three studies. Mistakes in the Sloan-Kettering press release were highlighted by a group of laetrile proponents led by Ralph Moss, former public affairs official of Sloan-Kettering hospital, who was fired when he announced his membership in the group. These mistakes were considered inconsequential, but Nicholas Wade in Science noted that "even the appearance of a departure from strict objectivity is unfortunate." The results from these studies were published all together.