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Laetrile, which achieved great notoriety during the 1970s and early 1980s, is the trade name for a synthetic relative of amygdalin, a chemical in the kernels of apricot pits, apple seeds, bitter almonds, and some other stone fruits and nuts. Many laetrile promoters have called it "vitamin B17" and falsely claimed that cancer is a vitamin deficiency disease that laetrile can cure. Claims for laetrile's efficacy have varied considerably . First it was claimed to prevent and cure cancer. Then it was claimed not to cure, but to "control" cancer while giving patients an increased feeling of well being. More recently, laetrile has been claimed to be effective, not by itself, but as one component of "metabolic therapy" (described below).
Laetrile was first used to treat cancer patients in California in the 1950s. According to proponents, it kills tumor cells selectively while leaving normal cells alone. Although laetrile has been promoted as safe and effective, clinical evidence indicates that it is neither . When subjected to enzymatic breakdown in the body, it forms glucose, benzaldehyde, and hydrogen cyanide . Some cancer patients treated with laetrile have suffered nausea, vomiting, headache and dizziness, and a few have died from cyanide poisoning. Laetrile has been tested in at least 20 animal tumor models and found to have no benefit either alone or together with other substances. Several case reviews have found no benefit for the treatment of cancer in humans.
In response to political pressure, a clinical trial was begun in 1982 by the Mayo Clinic and three other U.S. cancer centers under NCI sponsorship. Laetrile and "metabolic therapy" were administered as recommended by their promoters. The patients had advanced cancer for which no proven treatment was known. Of 178 patients, not one was cured or stabilized, and none had any lessening of any cancer-related symptoms. The median survival rate was about five months from the start of therapy. In those still alive after seven months, tumor size had increased. Several patients experienced symptoms of cyanide toxicity or had blood levels of cyanide approaching the lethal range .
In 1975, a class action suit was filed to stop the FDA from interfering with the sale and distribution of laetrile. Early in the case, a federal district court judge in Oklahoma issued orders allowing cancer patients to import a six-month supply of laetrile for personal use if they could obtain a physician's affidavit that they were "terminal." In 1979, the U.S. Supreme Court ruled that it is not possible to be certain who is terminal and that even if it were possible, both terminally ill patients and the general public deserve protection from fraudulent cures. In 1987, after further appeals were denied, the district judge (a strong proponent of laetrile) finally yielded to the higher courts and terminated the affidavit system . Few sources of laetrile are now available within the United States, but it still is utilized at several Mexican clinics.