The kernels of cherries and other fruits contain a chemical called amygdalin. A pure form of amygdalin is laetrile, sometimes called B-17, which some people promote as a treatment for cancer. B-17 is not a vitamin.
Proponents of B-17 (laetrile) for treating cancer claim that it can improve health, energy levels and well being, detoxify and cleanse the body, and prolong life. The main anti-cancer ingredient in laetrile is believed to be the poison called cyanide.
According to the National Cancer Institute and many other medical sources, there is no scientific evidence that laetrile is beneficial for treating cancer.
According to the New York University Langone Medical Center, possible side effects of laetrile include nausea, vomiting, headache, dizziness, bluish skin color, droopy eyelids, trouble walking, fever and confusion.
Laetrile is not approved by the U.S. Food and Drug Administration (FDA) and is illegal to bring into the United States.
Laetrile does occur naturally in many plants, including apricots, peaches, apple seeds, and lentils. For a positive review of laetrile, see Mary Laredo's "The Laetrile Saga," linked below.