Laetrile

Amygdalin (on the left) and its companion molecule laetrile (right) burst into the headlines in the 1950s as purported cancer cures. As scientific research soon determined, they are not effective for treating cancer—they are potent poisons.

Amygdalin occurs in many plants, notably in seeds of fruits in the Rosaceae family such as bitter almonds, apricots, and plums. Laetrile is a derivative of amygdalin formed by the hydrolytic removal of one glycoside group from the parent compound. The literature is a bit confusing because the names and laetrile sometimes are conflated. Both molecules are also erroneously termed vitamin B₁₇.

Chemists Walter Norman Haworth and Birkett Wylam at Durham University (Newcastle upon Tyne, UK) elucidated the structure of amygdalin and synthesized it in 1923. Haworth was awarded the 1937 Nobel Prize in Chemistry for 1938.

From the 1950s through the 1970s, both compounds, under the name laetrile, were heavily promoted as a cure for many types of cancer. Rogue physicians and others established clinics in Mexico to which desperate patients flocked to receive the “cure” and other ineffective treatments. Science, however, prevailed: Laetrile was never approved by the US Food and Drug Administration or the European Commission.

The nitrile groups in amygdalin and laetrile are labile and easily removed as the cyanide ion by β-glucosidase enzymes in the human body. Cyanide, of course, is highly toxic; it is surprising that the compounds’ oral toxicity is given the mild hazard statement “harmful if swallowed”.

In 1981, Irving J. Lerner at the University of Minnesota Medical School (Minneapolis) summarized the laetrile hoax thus: "All prior forms of cancer quackery . . . pale in comparison with the laetrile crusade, the slickest, most sophisticated, and certainly the most remunerative cancer quack promotion in medical history."