Amygdalin and Laetrile – History and Current Usage

Ernst Krebs on vitamin B17

Amygdalin (D-mandelonitrile-β-gentiobioside) is a cyanogenic glycoside present in the pits of many fruits and in numerous plants belonging to the Rosaceae family, such as Prunus persica (peach), Prunus armeniaca (apricot) and Prunus amygdalus amara (bitter almond). Cyanogenic glycosides, also known as “nitrilosides,” are a large group of secondary metabolites that are widely distributed in the plant kingdom, including many plants that are commonly consumed by humans. The chemical properties of amygdalin from bitter almond seeds were first described by the German chemists Liebig and Wohler in 1837 after having been isolated 7 years earlier by the French chemists Pierre-Jean Robiquet and A. F. Boutron-Charlard.

Amygdalin was later "rediscovered" in 1920 by California physician Dr. Ernst Theodore Krebs, Sr. His son, Dr. Ernst Krebs, Jr. through further research, developed the compound into the injectable chemical known as “Laetrile or B17.” Both amygdalin, and its patented form Laetrile, have been promoted and sold as "vitamin B-17", although neither compound is technically considered a “vitamin.” Laetrile is structurally different from its mother compound, amygdalin, and is an acronym (LAEvo-rotatory mandeloniTRILE beta-diglucoside) for a purified, semi-synthetic form of amygdalin. The "LAEvo" part references a purified form of amygdalin that turns polarized light in a left-turning direction. Dr. Krebs Jr. discovered that only this left-turning form of Laetrile was effective against cancer.1 "Laetrile" (with a capital "L") usually refers to the Krebses' original product, whose purification process was patented by them; "laetrile" (with a lower case "l") refers to the commercial form of amygdalin which is most likely a mixture of the left and right-turning forms, which the Krebses believed to be much less effective as a therapy for cancer. Natural amygdalin with the right turning configuration can be racemized to the unnatural form, neoamygdaline, during inexperienced extraction, bad packing or storage.

It is alleged that the clinical research performed by the NCI (mentioned later in this article) did not use the laevo form of Laetrile used by Dr. Krebs, and consequently their results reported “Laetrile” to be ineffective for cancer. The subject of Laetrile is very complex and will be only briefly discussed in this paper. Furthermore, the politics of Laetrile have created a strong bias against amygdalin, hampering further human research of this beneficial compound.

Cyanogenic glycosides, such as amygdalin and prunasin, are found in over 1000 species of plants and consequently are present in the tissues of animals that eat those plants. Amygdalin and prunasin are common among plants of the family Rosaceae, particularly the genus Prunus, Poaceae (grasses), Fabaceae (legumes), and in other food plants, including flaxseed and manioc. Amygdalin is particularly found in:

  • Seeds of fruits or kernels: apricot, cherry, apple, peach, nectarine, plum, pear, prune

  • Nuts: macadamia, bitter almond, walnuts

  • Beans: Burma, broad (Vicia faba), lentils (sprouted), mung (sprouted), Lima, scarlet runner, Rangoon

  • Berries: Nearly all wild berries - blackberry, elderberry, raspberry, cranberry, strawberry, chokeberry, Christmas berry

  • Grasses: wheat grass, acacia, alfalfa (sprouted), milkweed, Sudan, white Dover

  • Seeds: flax, chia, sesame

Many plants that contain high amounts of amygdalin have been an important part of the traditional diet and food medicine of several cultures for millennia. For example, bitter almonds and apricot kernels, have been used in traditional Chinese medicine (TCM) for centuries. In TCM, apricot kernels are considered to benefit the large intestine and lungs, and are used to stop cough and wheezing, moistens the intestines, and unblock the bowels.2, 3 Apricot seed-oil has been used traditionally as a laxative. Additionally, in TCM bitter almonds have historically been employed to remove “blood stasis,” and to treat abscesses and tumors.4 Amygdalin from bitter almonds and apricot kernels was used to treat cancer more than a century ago in Russia and later in North America. Amygdalin was one of the most popular, non-conventional, anti-cancer treatments in the U.S. by 1970s. By 1978, an estimated 70,000 U.S. cancer patients had used amygdalin and its purified, semi-synthetic form Laetrile and to treat their cancer.5 However, Laetrile and amygdalin are not approved by the U.S. Food and Drug Administration as a treatment for cancer.

Most people take amygdalin in the form of apricot kernels. However, like an apricot, in the middle of a peach is a hard shell. If you break open the hard shell with a “nut cracker,” pliers or hammer, you will find a small seed/kernel in the middle that looks like an almond. This peach kernel, is much softer than an almond, does not taste like an almond, and is also rich in amygdalin. Generally, the bitterness of an apricot, almond or peach kernel is indicative of its amygdalin content. The more bitter, the more amygdalin it contains. Both sweet and bitter almond varieties contain quantities of amygdalin. However, there can be a significant range of amygdalin content of the apricot kernels being sold as “bitter” varieties. It is best to find a reputable source and always use the same source to assure consistency of amygdalin content.

As with so many other useful chemicals that we get from plants, the evolutionary utility of cyanogenic glycosides like amygdalin and prunasin is for defense of the plant. The cyanogenic glycosides contained in plants deters grazers, from eating the valuable seeds and dispensable fruit in the plants. Along with playing a role in deterring herbivores, in some plants they control germination, bud formation, carbon and nitrogen transport, and possibly act as antioxidants. The production of cyanogenic glycosides is an evolutionarily conserved function, appearing in species as old as ferns and as recent as angiosperms.

Safety First

Verified cases of death from eating apricot kernels is extremely rare. I could find only three publications describing lethal consequences, all in children (these reports, however, are widely cited in anti-Laetrile publications). Sayre and Kaymakcalav