What is an Alkaloid?

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  • Written By: Marjorie McAtee
  • Edited By: W. Everett
  • Last Modified Date: 19 January 2020
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An alkaloid is a type of plant-derived organic compound. Alkaloids are generally composed of oxygen, hydrogen, carbon, and nitrogen. Some alkaloids are considered toxic, but others are often used medicinally. Alkaloids one might encounter in everyday life include caffeine, the drugs atropine and quinine, and the deadly nightshade plant.

Alkaloids are relatively rare in plants. They have what's considered to be a complex chemical structure, and they always contain a nitrogen molecule. An alkaloid may also contain molecules of oxygen, carbon, and hydrogen.

Though their effects vary from medicinal to poisonous, all alkaloids cause a physiological effect on the human body. Some alkaloids, such as the ergot alkaloid, can be toxic and even deadly. Cocaine and caffeine are two plant-based alkaloids believed to be toxic in their effects.

A class of alkaloids known as the tropane alkaloids are historically famous for their use as poisons. The alkaloid atropine belongs in this class. It is typically derived from the plant atropa belladonna or deadly nightshade.

Many alkaloids can be used for medical purposes. Atropine, believed to have been used historically as a poison, is now sometimes used to stimulate the central nervous system and dilate the pupils of the eyes. Scopolamine, an alkaloid of the same class, is often used to treat motion sickness. Quinine, one of 31 alkaloid chemical compounds found in the plant cinchona succirubra, has antimalarial properties. Quinine is still used as a treatment of choice for malaria.


Some alkaloids, such as the morphine alkaloids, can have narcotic effects. These alkaloids are typically derived from the opium poppy. Morphine alkaloids may be some of the oldest drugs in the world. Their use was first recorded in Sumeria circa 3500 B.C. Morphine alkaloids were often used to induce drowsiness in laudanum preparations from the 1830s onward, even though they were believed to be addictive. Today, morphine alkaloids are still sometimes used in medicine as an analgesic, or pain reliever.

Vincristine, an alkaloid believed to have been first isolated from catharanthus roseus in the 1950s, is now used to treat non-Hodgkin's lymphoma and childhood leukemia. Vinblastine, also isolated from the same plant, is believed to be an effective treatment for Hodgkin's disease.


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