The bitter almond tree, originating in Asia and Africa, is outlawed in the U.S. because of the toxic chemicals contained in the nut. Cyanide poisoning results when large amounts of the nuts are consumed.
Removing the bitter almond oil from its shell and crushing its leaves produces an oil containing prussic acid, also known as cyanide. This oil (almond essence) has been known to kill humans in amounts as small as 7-1/2 ml. Allergies to bitter almond result in cyanide poisoning symptoms and sometimes death.
Bitter almond contains amygdalin, from which is derived laetrile. Amygdalin releases cyanide when exposed to an enzyme found in the seed and the human digestive system. For this reason, bitter almond is banned in Europe and the U.S.
In spite of potential toxicity, bitter almond was used in the U.S. in the 1920s for its believed cancer fighting properties. It was used as early as the 1800s in Russia and France. Production and use as a cancer fighting medicine continues in Mexico.