The term “ laetrile ” is an acronym (laevorotatory and mandelonitrile) used to describe a purified form of the chemical amygdalin, a cyanogenic glucoside (a plant compound that contains sugar and produces cyanide) found in the pits of many fruits and raw nuts and in other plants such as lima beans, clover, and sorghum. Reviewed in [1-6] In the 1970s, laetrile gained popularity as an anticancer agent. By 1978, more than 70,000 individuals in the United States were reported to have been treated with it. Reviewed in [2,7,8] Laetrile has been used for cancer treatment both as a single agent and in combination with a metabolic therapy program that consists of a specialized diet, high-dose vitamin supplements, and pancreatic enzymes. Reviewed in 
In the United States, researchers must file an Investigational New Drug (IND) application with the U.S. Food and Drug Administration (FDA) to conduct drug research in human subjects. In 1970, an application for an IND to study laetrile was filed by the McNaughton Foundation (San Ysidro, California). This request was initially approved but later rejected because preclinical evidence in animals showed that laetrile was not likely to be effective as an anticancer agent, Reviewed in [3,11,12] and because there were questions about how the proposed study was to be conducted. Reviewed in  Laetrile supporters viewed this reversal as an attempt by the U.S. government to block access to new and promising cancer therapies, and pressure mounted to make laetrile available to the public. Court cases in Oklahoma, Massachusetts, New Jersey, and California challenged the FDA’s role in determining which drugs should be available to cancer patients. Consequently, laetrile was legalized in more than 20 states during the 1970s. In 1980, the U.S. Supreme Court overturned decisions by the lower courts, thereby reaffirming the FDA’s position that drugs must be proven to be both safe and effective before widespread public use. Reviewed in [2,14] As a result, the use of laetrile as a cancer therapy or as a treatment for any other medical condition is not approved in the United States, but the compound continues to be manufactured and administered as an anticancer therapy, primarily in Mexico.
Although the names laetrile, Laetrile, and amygdalin are often used interchangeably, they are not the same product. The chemical composition of U.S.-patented Laetrile (mandelonitrile-beta-glucuronide), a semisynthetic derivative of amygdalin, is different from the laetrile/amygdalin produced in Mexico (mandelonitrile beta-D-gentiobioside), which is made from crushed apricot pits. Reviewed in [15,16] Mandelonitrile, which contains cyanide, is a structural component of both products. Reviewed in  It has been proposed that cyanide is the active cancer-killing ingredient in laetrile, but two other breakdown products of amygdalin—prunasin (which is similar in structure to Laetrile) and benzaldehyde —may also be cancer cell inhibitors.[17-20] The studies discussed in this summary used either Mexican laetrile/amygdalin or the patented form. In most instances, the generic term “laetrile” will be used in this summary; however, a distinction will be made between the products when necessary.
Laetrile can be administered orally as a pill, or it can be given by injection (intravenous or intramuscular). It is commonly given intravenously for a period of time followed by oral maintenance therapy. The incidence of cyanide poisoning is much higher when laetrile is taken orally  Reviewed in [22,23] because intestinal bacteria and some commonly eaten plants contain enzymes (beta-glucosidases) that activate the release of cyanide after laetrile has been ingested. Reviewed in [17,22] Relatively little breakdown occurs to yield the cyanide when laetrile is injected. Reviewed in [7,22] Administration schedules and the length of treatment in animal models and humans vary widely.References
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