Any of a number of physiologically active and frequently poisonous substances contained in some plants and fungi. They are usually organic bases and contain nitrogen. They form salts with acids and, when soluble, give alkaline solutions.
Substances in this group are included by custom rather than by scientific rules. Examples include morphine, cocaine, quinine, caffeine, strychnine, nicotine, and atropine.
Alkaloids are obtained by cutting up the plants and macerating the mass with acidified water in a conical vat, where a layer of lint receives the percolated liquid. If the alkaloid is volatile, it is separated with steam after making the mixture alkaline; if insoluble, it may be obtained by filtration, after which it may be purified by crystallization.
Opium alkaloids include morphine, codeine and papaverine. Morphine is a well known pain killer and codeine is used in the treatment of coughs. Papaverine, unlike the others, is nonaddictive. It is antispasmodic and vascodilatory. Tropane alkaloids have certain common structural features. Examples include atropine, used as an antidote for some nerve gases, and cocaine, the first local anaesthetic used medicinally. Cinchona bark alkaloids include quinine, a drug which cures malaria, formerly one of the world's most widespread diseases. The drug comes from the cinchona tree found on the eastern slopes of the Andes Mountains. Rauwolfia alkaloids, produced from the roots of a shrub found in India, include reserpine, which is widely used as a tranquillizer and sedative. Sterol alkaloids are many in number, one example being solanine, a glycoside found in potato shoots.
In 1992, epibatidine, a chemical extracted from the skin of an Ecuadorean frog, was identified as a member of an entirely new class of alkaloid. It is an organochlorine compound, which is rarely found in animals, and a powerful painkiller, about 200 times as effective as morphine.