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Alkaloids are difficult to define because they do not represent a homogeneous group of compounds from either the chemical, biochemical, or physiologic viewpoint. Consequently, except for the fact they are all organic nitrogenous compounds, reservations must be appended to any general definition. All alkaloids occur in plants, but some are found in animals, and most have been reproduced in the laboratory by chemical synthesis.

Most possess basic properties, owing to the presence of an amino nitrogen, and many, especially those pertinent to pharmacy and medicine, are very bitter and possess marked physiologic activity. Despite the difficulties attending a precise definition, the term alkaloid is extremely useful and is commonly applied to basic nitrogenous compounds of physiologically active plant origin.

Alkaloids may occur in various parts of the plant. For example, they are found in: the seeds of physostigma and areca; the fruits of conium; the leaves of belladonna and coca; the underground stems of sanguinaria; the roots of ipecac and hydrastis; and the barks of cinchona. They are also found in fungi such as ergot and Amanita citrina.

Aconitum species (e.g. Monkshood, used extensively in Chinese medicine) are among the most poisonous plants known. As little as 2 mg of the pure alkaloid can be fatal.

Examples include: LSD, morphine and Deadly Nightshade.


Blumenthal, M (Ed.): The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council. Austin, TX. 1998.

Tyler, V.E., L.R. Brady, et.al. 1981. Pharmacognosy. Lea and Febiger, Philadelphia. 520.


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