Alkaloid, a chemical substance of plant origin composed of carbon, hydrogen, nitrogen, and (usually) oxygen. The alkaloids are organic bases similar to the alkalies (inorganic bases); the name means alkali-like. Most alkaloids have pronounced effects on the nervous system of humans and other animals. Many are used as drugs. Some familiar alkaloids are caffeine, nicotine, quinine, cocaine, and morphine.
Alkaloids occur mainly in various genera of seed plants, such as the opium poppy and tobacco plant. Alkaloids can be found in almost all parts of these plants, including the leaves, roots, seeds, and bark. Each plant part usually contains several chemically related alkaloids. The function of alkaloids in plant metabolism is not known. Of the hundreds of alkaloids found in nature, only about 30 are used commercially.
Alkaloids must be extracted from plants before they can be used. After the plants have been dried and crushed, chemical reagents such as alcohol and dilute acids are used to extract the alkaloid content from the plant material. Pure alkaloid extracts are usually bitter, colorless solids. Some alkaloids, such as reserpine and morphine, are synthesized (produced artificially).
Some alkaloids, such as nicotine, are used in pesticides, and others are used as chemical reagents. The primary use of alkaloids, however, is in medicine, because they can act quickly on specific areas of the nervous system. Alkaloids are the active components of many anesthetics, sedatives, stimulants, relaxants, and tranquilizers. They are taken by mouth and administered by injection. Except under a physician's supervision, use of alkaloids is dangerous, because most are habit-forming (for example, almost all narcotics are alkaloids) and large doses can be poisonous.
Strychnine, used in small doses as a stimulant and a tonic, is highly poisonous. Quinine, used in treating malaria, can cause dizziness if taken in large doses. Morphine and cocaine are among the most effective drugs known for temporarily relieving pain without causing loss of consciousness. However, these two alkaloids are habit-forming and can be harmful if their use is continued. Curare, used as a muscle-relaxing drug and in arrow poisons used by South American Indians, is a mixture of various alkaloids.
In most cases, the extraction of natural alkaloids and the synthesis of alkaloids are complicated, costly processes. Furthermore, alkaloid drugs usually produce unpleasant side effects. For these reasons, several synthetic compounds have been developed for use as alkaloid substitutes. For example, Novocain (a trade name for procaine) is often used instead of cocaine, and Demerol (a trade name for meperidine) is often substituted for morphine. Alkaloid substitutes are usually less toxic than alkaloids, but are also generally less potent.