Laetrile treatment for cancer: risk of cyanide poisoning

Cochrane: Laetrile is a word created from the first letters of laevorotatory and mandelonitrile and describes a semi-synthetic form of amygdalin. Amygdalin is a compound that can be isolated from the seeds of many fruits such as peaches, bitter almonds and apricots. Both laetrile and amygdalin have a common structural component, mandelonitrile, that contains cyanide.

The lack of laetrile's effectiveness and the risk of side effects from cyanide poisoning led the Food and Drugs Agency (FDA) in the US and the European Commission to ban its use. However, it is possible to buy laetrile or amygdalin via the Internet. As there is no government control of these markets, preparations may not only come from questionable sources but they may also be contaminated. Cancer patients should be informed about the high risk of developing serious adverse effects due to cyanide poisoning after laetrile or amygdalin, especially after oral ingestion. This risk could increase with concomitant intake of vitamin C and in vegetarians with vitamin B12 deficiency.
This systematic review found that there is no reliable evidence for the alleged effects of laetrile or amygdalin for curative effects in cancer patients.

The claims that laetrile or amygdalin have beneficial effects for cancer patients are not currently supported by sound clinical data. There is a considerable risk of serious adverse effects from cyanide poisoning after laetrile or amygdalin, especially after oral ingestion. The risk–benefit balance of laetrile or amygdalin as a treatment for cancer is therefore unambiguously negative.