Amygdalin the so-called safe and natural anticancer vitamin B17, is none of those things. It is not a vitamin in any sense of the word. It has no anticancer properties. It is poisonous.
The compound, formula C20H27NO11, is a glycoside initially isolated from the seeds of the tree Prunus dulcis in the nineteenth century, also known as bitter almonds. Enzymes (namely glucosidases) found in the gut and in some foods break down amygdalin to release hydrogen cyanide. See also synthetic derivative, laetrile.
“Cochrane Collaboration” had this to say:
“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.”
Milazzo S., Ernst E., Lejeune S., Boehm K., Horneber M. & Milazzo S. (2011). Laetrile treatment for cancer, DOI: 10.1002/14651858.CD005476.pub3