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Laetrile/Amygdalin (PDQ®): Complementary and alternative medicine - Health Professional Information [NCI] - Laboratory / Animal / Preclinical Studies


The toxicity of laetrile appears to be dependent on the route of administration. Oral administration is associated with much greater toxicity than intravenous, intraperitoneal, or intramuscular injection.[1,6,14,21] Reviewed in [9,10,22,23] As noted previously (refer to the History section of this summary for more information), most mammalian cells contain only trace amounts of the enzyme beta-glucosidase;[24] however, this enzyme is present in gastrointestinal tract bacteria and in many food plants. Reviewed in [6,9,15,25,26,27] Two studies have specifically examined the role of intestinal bacteria in the breakdown of orally administered amygdalin.[9,28] In one study, rats bred and raised under germ-free conditions and rats bred and raised under normal conditions were given oral amygdalin. The germ-free rats exhibited no side effects from the compound, and their blood concentrations of cyanide were indistinguishable from those of untreated rats. Many of the rats with normal quantities of intestinal bacteria showed signs of cyanide poisoning (e.g., lethargy and convulsions), and they had high levels of cyanide in their blood. In the second study, rats were either treated or not treated with the antibiotic neomycin before being given oral amygdalin.[6] In this study, urinary excretion of detoxified cyanide (i.e., thiocyanate) was measured. The amount of urinary thiocyanate was 40 times higher in rats that had not been given the antibiotic, indicating that more amygdalin had been broken down in animals with normal amounts of intestinal bacteria. In humans, as in rats, substantial breakdown of amygdalin occurs in the intestines; however, little breakdown of either intravenously or intramuscularly delivered amygdalin occurs in humans, with most of the intact compound eventually excreted in urine.[26,29]


  1. Gostomski FE: The effects of amygdalin on the Krebs-2 carcinoma and adult and fetal DUB(ICR) mice. [Abstract] Diss Abstr Int B 39 (5): 2075-B, 1978.
  2. Wodinsky I, Swiniarski JK: Antitumor activity of amygdalin MF (NSC-15780) as a single agent and with beta-glucosidase (NSC-128056) on a spectrum of transplantable rodent tumors. Cancer Chemother Rep 59 (5): 939-50, 1975 Sep-Oct.
  3. Laster WR Jr, Schabel FM Jr: Experimental studies of the antitumor activity of amygdalin MF (NSC-15780) alone and in combination with beta-glucosidase (NSC-128056). Cancer Chemother Rep 59 (5): 951-65, 1975 Sep-Oct.
  4. Stock CC, Tarnowski GS, Schmid FA, et al.: Antitumor tests of amygdalin in transplantable animal tumor systems. J Surg Oncol 10 (2): 81-8, 1978.
  5. Menon MM, Bhide SV: Perinatal carcinogenicity of isoniazid (INH) in Swiss mice. J Cancer Res Clin Oncol 105 (3): 258-61, 1983.
  6. Newton GW, Schmidt ES, Lewis JP, et al.: Amygdalin toxicity studies in rats predict chronic cyanide poisoning in humans. West J Med 134 (2): 97-103, 1981.
  7. Hill GJ 2nd, Shine TE, Hill HZ, et al.: Failure of amygdalin to arrest B16 melanoma and BW5147 AKR leukemia. Cancer Res 36 (6): 2102-7, 1976.
  8. Lea MA, Koch MR: Effects of cyanate, thiocyanate, and amygdalin on metabolite uptake in normal and neoplastic tissues of the rat. J Natl Cancer Inst 63 (5): 1279-83, 1979.
  9. Carter JH, McLafferty MA, Goldman P: Role of the gastrointestinal microflora in amygdalin (laetrile)-induced cyanide toxicity. Biochem Pharmacol 29 (3): 301-4, 1980.
  10. Khandekar JD, Edelman H: Studies of amygdalin (laetrile) toxicity in rodents. JAMA 242 (2): 169-71, 1979.
  11. Manner HW, DiSanti SJ, Maggio MI, et al.: Amygdalin, vitamin A and enzyme induced regression of murine mammary adenocarcinomas. J Manipulative Physiol Ther 1 (4): 246-8, 1978.
  12. Ovejera AA, Houchens DP, Barker AD, et al.: Inactivity of DL-amygdalin against human breast and colon tumor xenografts in athymic (nude) mice. Cancer Treat Rep 62 (4): 576-8, 1978.
  13. Lewis JP: Laetrile. West J Med 127 (1): 55-62, 1977.
  14. Schmidt ES, Newton GW, Sanders SM, et al.: Laetrile toxicity studies in dogs. JAMA 239 (10): 943-7, 1978.
  15. Dorr RT, Paxinos J: The current status of laetrile. Ann Intern Med 89 (3): 389-97, 1978.
  16. Levi L, French WN, Bickis IJ, et al.: Laetrile: a study of its physicochemical and biochemical properties. Can Med Assoc J 92 (20): 1057-61, 1965.
  17. Biaglow JE, Durand RE: The enhanced radiation response of an in vitro tumour model by cyanide released from hydrolysed amygdalin. Int J Radiat Biol Relat Stud Phys Chem Med 33 (4): 397-401, 1978.
  18. Bhatti RA, Ablin RJ, Guinan PD: Tumour-associated directed immunity in prostatic cancer: effect of amygdalin. IRCS Med Sci Biochem 9 (1): 19, 1981.
  19. Koeffler HP, Lowe L, Golde DW: Amygdalin (Laetrile): effect on clonogenic cells from human myeloid leukemia cell lines and normal human marrow. Cancer Treat Rep 64 (1): 105-9, 1980.
  20. Syrigos KN, Rowlinson-Busza G, Epenetos AA: In vitro cytotoxicity following specific activation of amygdalin by beta-glucosidase conjugated to a bladder cancer-associated monoclonal antibody. Int J Cancer 78 (6): 712-9, 1998.
  21. Moertel CG, Ames MM, Kovach JS, et al.: A pharmacologic and toxicological study of amygdalin. JAMA 245 (6): 591-4, 1981.
  22. Newmark J, Brady RO, Grimley PM, et al.: Amygdalin (Laetrile) and prunasin beta-glucosidases: distribution in germ-free rat and in human tumor tissue. Proc Natl Acad Sci U S A 78 (10): 6513-6, 1981.
  23. Navarro MD: Five years experience with laetrile therapy in advanced cancer. Acta Unio Int Contr Cancrum 15(suppl 1): 209-21, 1959.
  24. Conchie J, Findlay J, Levvy GA: Mammalian glycosidases: distribution in the body. Biochem J 71 (2): 318-25, 1959.
  25. Herbert V: Laetrile: the cult of cyanide. Promoting poison for profit. Am J Clin Nutr 32 (5): 1121-58, 1979.
  26. Ames MM, Moyer TP, Kovach JS, et al.: Pharmacology of amygdalin (laetrile) in cancer patients. Cancer Chemother Pharmacol 6 (1): 51-7, 1981.
  27. Unproven methods of cancer management. Laetrile. CA Cancer J Clin 22 (4): 245-50, 1972 Jul-Aug.
  28. Shils ME, Hermann MG: Unproved dietary claims in the treatment of patients with cancer. Bull N Y Acad Med 58 (3): 323-40, 1982.
  29. Ames MM, Kovach JS, Flora KP: Initial pharmacologic studies of amygdalin (laetrile) in man. Res Commun Chem Pathol Pharmacol 22 (1): 175-85, 1978.

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Last Updated: February 25, 2014
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