Laetrile is a name for the chemical amygdalin. It is derived from the pits of apricots and peaches, and from other fruits.

In the 1920s, Dr. Ernst T. Krebs developed the idea that laetrile might selectively destroy cancer cells. His son Ernst T. Krebs Jr., later classified the substance "vitamin B17". The two of them introduced the idea that cancer cells had an enzyme that healthy cells lacked in the same abundance, and that this enzyme acted on laetrile to produce cytotoxic cyanide. Laetrile was touted as an alternative cure for cancer.

This hypothesis and the classification of laetrile as a vitamin were later proven untrue when laetrile was subjected to scientific scrutiny in the 1970s. Investigations showed that anecdotal reports of improvement, but this was attributed to a placebo effect. As a drug, laetrile was shown by clinical trials to have no effect on tumor or on prolonging life. Some patients got cyanide poisoning. (Cyanide is naturally produced in the intestines when laetrile is acted upon by intestinal bacteria.)

The Food and Drug Administration labeled laetrile a fraud, making it illegal to ship it accross state lines or to import it from other countries. However the chemical itself is still legal in some states and in Mexico.