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any of a class of organic compounds composed of carbon, hydrogen, nitrogen, and usually oxygen that are often derived from plants. Although the name means alkalilike, some alkaloids do not exhibit alkaline properties. Many alkaloids, though poisons, have physiological effects that render them valuable as medicines. For example, curarine, found in the deadly extract curarecurare
, any of a variety of substances originally used as arrow poisons by Native South Americans in hunting and in warfare. The main active substance of curare, tubocurarine, is an alkaloid extracted from Chondodendron tomentosum, Strychnos toxifera,
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, is a powerful muscle relaxant; atropineatropine
, alkaloid drug derived from belladonna and other plants of the family Solanaceae (nightshade family). Available either as the tincture or extract of belladonna, or as the pure substance atropine sulfate, it is a depressant of the parasympathetic nervous system.
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 is used to dilate the pupils of the eyes; and physostigmine is a specific for certain muscular diseases. Narcotic alkaloids used in medicine include morphinemorphine,
principal derivative of opium, which is the juice in the unripe seed pods of the opium poppy, Papaver somniferum. It was first isolated from opium in 1803 by the German pharmacist F. W. A. Sertürner, who named it after Morpheus, the god of dreams.
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 and codeinecodeine
, alkaloid found in opium. It is a narcotic whose effects, though less potent, resemble those of morphine. An effective cough suppressant, it is mainly used in cough medicines. Like other narcotics, codeine is addictive. See drug addiction and drug abuse.
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 for the relief of pain and cocainecocaine
, alkaloid drug derived from the leaves of the coca shrub. A commonly abused illegal drug, cocaine has limited medical uses, most often in surgical applications that take advantage of the fact that, in addition to its anesthetic effect, it constricts small arteries,
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 as a local anesthetic. Other common alkaloids include quininequinine
, white crystalline alkaloid with a bitter taste. Before the development of more effective synthetic drugs such as quinacrine, chloroquine, and primaquine, quinine was the specific agent in the treatment of malaria.
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, caffeinecaffeine
, odorless, slightly bitter alkaloid found in coffee, tea, kola nuts (see cola), ilex plants (the source of the Latin American drink maté), and, in small amounts, in cocoa (see cacao). It can also be prepared synthetically from uric acid.
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, nicotinenicotine,
C10H14N2, poisonous, pale yellow, oily liquid alkaloid with a pungent odor and an acrid taste. It turns brown on exposure to air. Nicotine, a naturally occurring constituent of tobacco, is the active ingredient in tobacco smoke.
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, strychninestrychnine
, bitter alkaloid drug derived from the seeds of a tree, Strychnos nux-vomica, native to Sri Lanka, Australia, and India. It has been used as a rat poison for five centuries, and rat biscuits still remain a cause of accidental poisoning in humans.
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, serotoninserotonin
, organic compound that was first recognized as a powerful vasoconstrictor occurring in blood serum. It was partially purified, crystallized, and named in 1948, and its structure was deduced a year later.
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, and LSDLSD
or lysergic acid diethylamide
, alkaloid synthesized from lysergic acid, which is found in the fungus ergot (Claviceps purpurea). It is a hallucinogenic drug that intensifies sense perceptions and produces hallucinations, mood changes, and changes in the
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. Aconitine is the alkaloid of aconiteaconite
, monkshood,
or wolfsbane,
any of several species of the genus Aconitum of the family Ranunculaceae (buttercup family), hardy perennial plants of the north temperate zone, growing wild or cultivated for ornamental or medicinal purposes.
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. Cinchonine and quinine are derived from cinchonacinchona
or chinchona
, name for species of the genus Cinchona, evergreen trees of the madder family native to the Andean highlands from Bolivia to Colombia and also to some mountainous regions of Panama and Costa Rica.
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, coniine is found in poison hemlockhemlock,
any tree of the genus Tsuga, coniferous evergreens of the family Pinaceae (pine family) native to North America and Asia. The common hemlock of E North America is the eastern hemlock, T.
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, and reserpine is an extract of rauwolfia roots. Emetine is an alkaloid of ipecacipecac
, drug obtained from the dried roots of a creeping shrub, Cephaelis (or Psychotria) ipecacuanha, native to Brazil but cultivated in other tropical climates.
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A cyclic organic compound that contains nitrogen in a negative oxidation state and is of limited distribution among living organisms. Over 10,000 alkaloids of many different structural types are known; and no other class of natural products possesses such an enormous variety of structures. Therefore, alkaloids are difficult to differentiate from other types of organic nitrogen-containing compounds.

Simple low-molecular-weight derivatives of ammonia, as well as polyamines and acyclic amides, are not considered alkaloids because they lack a cyclic structure in some part of the molecule. Amines, amine oxides, amides, and quaternary ammonium salts are included in the alkaloid group because their nitrogen is in a negative oxidation state (the oxidation state designates the positive or negative character of atoms in a molecule). Nitro and nitroso compounds are excluded as alkaloids. The almost-ubiquitous nitrogenous compounds, such as amino acids, amino sugars, peptides, proteins, nucleic acids, nucleotides, prophyrins, and vitamins, are not alkaloids. However, compounds that are exceptions to the classical-type definition (that is, a compound containing nitrogen, usually a cyclic amine, and occurring as a secondary metabolite), such as neutral alkaloids (colchicine, piperine), the β-phenyl-ethylanines, and the purine bases (caffeine, theophylline, theobromine), are accepted as alkaloids.

Alkaloids often occur as salts of plant acids such as malic, meconic, and quinic acids. Some plant alkaloids are combined with sugars, for example, solanine in potato (Solanum tuberosum) and tomatine in tomato (Lycopersicum esculentum). Others occur as amides, for example, piperine from black pepper (Piper nigrum), or as esters, for example, cocaine from coca leaves (Erythroxylum coca). Still other alkaloids occur as quaternary salts or tertiary amine oxides.

While most alkaloids have been isolated from plants, a large number have been isolated from animal sources. They occur in mammals, anurans (frogs, toads), salamanders, arthropods (ants, millipedes, ladybugs, beetles, butterflies), marine organisms, mosses, fungi, and certain bacteria.

Many alkaloids exhibit marked pharmacological activity, and some find important uses in medicine. Atropine, the optically inactive form of hyoscyamine, is used widely in medicine as an antidote to cholinesterase inhibitors such as physostigmine and insecticides of the organophosphate type; it is also used in drying cough secretions. Morphine and codeine are narcotic analgesics, and codeine is also an antitussive agent, less toxic and less habit-forming than morphine. Colchicine, from the corms and seeds of the autumn crocus, is used as a gout suppressant. Caffeine, which occurs in coffee, tea, cocoa, and cola, is a central nervous system stimulant; it is used as a cardiac and respiratory stimulant and as an antidote to barbiturate and morphine poisoning. Emetine, the key alkaloid of ipecac root (Cephaelis ipecacuanha), is used in the treatment of amebic dysentery and other protozoal infections.

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Epinephrine or adrenaline (see structure), produced in most animal species by the adrenal medulla, is used as a bronchodilator and cardiac stimulant and to counter allergic reactions, anesthesia, and cardiac arrest. See Epinephrine


(organic chemistry)
One of a group of nitrogenous bases of plant origin, such as nicotine, cocaine, and morphine.


any of a group of nitrogenous basic compounds found in plants, typically insoluble in water and physiologically active. Common examples are morphine, strychnine, quinine, nicotine, and caffeine
References in periodicals archive ?
Conclusion: The present study demonstrated that the alkaloid extract from MS alleviates ethanol withdrawal severity with no side effect on REM sleep.
Investigation of the alkaloid content of Rauwolfia serpentina root from regenerated plants.
In the herb segment, in 2011, Alkaloid launched successful cooperation with two more US companies, Arbonne International and Swanson, specializing in production and distribution of teas and products made of natural herbs.
Over the years, scientists have identified and isolated about 900 alkaloids from the skin of poison frogs.
It is interesting to note that both the number of implantation sites and corpora lutea decreased in the alkaloid-treated animals when the process of implantation ought to have been completed (implantation takes place normally within 5-6 days post-coitus in rats) before the exposure of the animals to the alkaloid mixture (treatment commenced from day 10 of pregnancy).
All doses of alkaloid fraction of leaves of Achyranthesaspera Linn given induced expression of p53 and inhibit production of CDK in protein mammary cancer cells (table 2 and table 3).
Results showed a high correlation between the total oxindole alkaloid content and the antiproliferative activity of the preparations.
They modified the gene for one enzyme involved in an early stage of the process so that it retained its role in making alkaloids, but acted on different starting compounds than it does naturally.
The alkaloid composition and the pharmacological properties of the two species are not identical.
The phytochemical data for each alkaloid provide information about its biosynthesis.
So how is it then that the caterpillar of the salt marsh moth frolics on the leaves of pyrrolizidine alkaloid producing plants and even makes a meal of them?