There is no vitamin B17. The term is inaccurately applied to laetrile, a discredited cancer drug, and amygdalin, the natural substance from which laetrile is made. Amygdalin occurs in the seeds of apricot, peaches, and almonds. Despite the lack of proof that laetrile/amygdalin works, promoters have continued to make unwarranted claims for it, referring to it as vitamin B17 and selling it as a dietary supplement to prevent, as well as treat, cancer. I've also seen promotions that claim these compounds can prevent and treat high blood pressure and arthritis.
I know of no scientific studies supporting those claims. One laetrile-related theory holds that cancer is a vitamin deficiency and that the missing vitamin is B17. That is nonsense. To fit the accepted scientific definition of a vitamin, a substance must be proven to be essential to achieving or maintaining good health. There is no need for amygdalin or laetrile in human nutrition.
In fact, instead of helping you, it may hurt you: laetrile and amygdalin can be converted to cyanide in the body, and laetrile use has been linked to several cases of cyanide toxicity. According to the American Cancer Society (ACS) one case report suggests that vitamin C may increase the amount of cyanide released from laetrile in the body, raising this risk. In addition, the ACS warns that individuals who also eat raw almonds or crushed fruit pits while taking laetrile and those who eat fruits and vegetables that contain the enzyme beta-glucosidase (such as celery, peaches, bean sprouts, and carrots) are more likely to experience toxicity.
You don't need "vitamin B17" to prevent cancer, to treat cancer or to prevent any other health problem, and you certainly don't need it to maintain good health. Avoid it.
Andrew Weil, M.D.