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Medicinal plants - Реферат


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Medicinal plants

Herbalism, also known as phytotherapy, is folk and traditional medicinalpractice based on the use of plantsand plant extracts.

Finding healing powers in plants is an ancient idea. People in all continents have long used hundreds, if not thousands, of indigenous plants, for treatment of various ailments dating back to prehistory. There is evidence that Neanderthals living 60,000 years ago in present-day Iraq used plants for medicinal purposes. These plants are still widely used in ethnomedicine around the world.

Plants have an almost limitless ability to synthesize aromatic substances, most of which are phenols or their oxygen-substituted derivatives such as tannins. Most are secondary metabolites, of which at least 12,000 have been isolated, a number estimated to be less than 10% of the total. In many cases, these substances serve as plant defense mechanisms against predation by microorganisms, insects, and herbivores. Many of the herbs and spices used by humans to season food yield useful medicinal compounds.

The use and search for drugs and dietary supplements derived from plants have accelerated in recent years. Pharmacologists, microbiologists, botanists, and natural-products chemists are combing the Earth for phytochemicals and leads that could be developed for treatment of various diseases.--Dr M Tariq Salman 19:06, 30 January 2006 (UTC)

The use of herbsto treat diseaseis almost universal among non-industrialized societies. A number of traditions came to dominate the practise of herbal medicine in the Western worldat the end of the twentieth century:

  • The Western, based on Greekand Romansources,

  • The Ayurvedicfrom India, and

  • Chinese herbal medicine(Chinese herbology).

  • Many of the pharmaceuticalscurrently available to Western physicians have a long history of use as herbal remedies, including opium, aspirin, digitalis, and quinine.

Biological background

All plants produce chemical compoundsas part of their normal metabolicactivities. These can be split into primary metabolites, such as sugarsand fats, found in all plants, and secondary metabolites found in a smaller range of plants, some only in a particular genusor species.

The autologousfunctions of secondary metabolites are varied. For example, as toxinsto deter predation, or to attract insects for pollination. It is these secondary metabolites which can have therapeutic actions in humans and which can be refined to produce drugs. Some examples are inulinfrom the roots of dahlias, quininefrom the cinchona, morphineand codeinefrom the poppy, and digoxinfrom the foxglove.

As of 2004, the National Center for Complementary and Alternative Medicine started to fund clinical trialsinto the effectiveness of herbal medicine.

Some surveys of scientific herbal medicine can be found in Evidence-based herbal medicine edited by Michael Rotblatt, Irwin Ziment; Philadelphia: Hanley & Belfus, 2002, and Herbal and traditional medicine: molecular aspects of health, edited by Lester Packer, Choon Nam Ong, Barry Halliwell; New York: Marcel Dekker, 2004.


A survey released in May 2004 by the National Center for Complementary and Alternative Medicinefocused on who used complementary and alternative medicines(CAM), what was used, and why it was used. The survey was limited to adults age 18 years and over during 2002 living in the United States. According to this recent survey, herbal therapy, or use of natural products other than vitaminsand minerals, was the most commonly used CAM therapy (18.9%)when all use of prayerwas excluded.


Examples of some commonly used herbal medicines:

  • Artichokeand several other plants reduced total serum cholesterollevels in preliminary studies.

  • Black cohoshand other plants that contain phytoestrogens(plant molecules with estrogenactivity) have some benefits for treatment of symptoms resulting from menopause.

  • Echinaceaextracts limit the length of coldsin some clinical trials, although some studies have found it to have no effect.

  • Garliclowers total cholesterol levels, mildly reduces blood pressure, reduces platelet aggregation, and has antibacterialproperties.

  • St John's wortis more effective than a placebofor the treatment of mild to moderate depressionin some clinical trials.

  • Peppermint teafor problems with the digestive tract, including irritable bowel syndromeand nausea.

  • Nigella sativa(Black cumin)is a generalist medicinal plant used for diverse ailments such as cough, pulmonary infections, asthma, influenza, allergy, hypertension and stomach ache. The seeds are considered carminative, stimulant, diuretic and galactogogue. It is often taken with honey. Seed powder or oil is externally applied for eruptions of skin.


A common misconception about herbalism and the use of 'natural' products in general, is that 'natural' equals safe. Nature, however, is not benign, and many plants have chemical defence mechanisms against predators that can have adverse effects on humans. Examples are poison hemlockand nightshade, which can be deadly. Herbs can also have undesirable side-effects just as pharmaceutical products can. These problems are exacerbated by lack of control over dosage and purity.

Name confusion

The common names of herbs may be shared with others with different effects. For example, in one case in Belgiumin a TCM-remedy for losing weight, one herb was swapped for another resulting in kidneydamage. One variety of the herb causes elevated blood pressure and increased heart rate, versus another variety for the weight-loss remedy, the varieties are differentiated by the suffix in the Latinnames.

International standards

The legal status of herbal ingredients varies by country. For example, Ayurvedicherbal products often contain levels of heavy metals that are considered unsafe in the US, but heavy metals are considered therapeutic in Ayurvedic medicine.

Medical interaction

Those wishing to use herbal remedies should first consult with a physician, as some herbal remedies have the potential to cause adverse drug interactions when used in combination with various prescription and over-the-counterpharmaceuticals. Dangerously low blood pressure may result from the combination of an herbal remedy that lowers blood pressure together with prescription medicine that has the same effect. Physicians may not be the best sources of information because most have no knowledge of herbal medicine. There is little known about interactions of herbal remedies with pharmaceuticals because, contrary to pharmaceutical medicine, there is no official system, database, or hotline to report and publish adverse interactions, so even herbalists may not be aware of adverse interactions.

To put the safety issue in perspective, an editorial in the British Medical Journalpointed out, "Even though herbal medicines are not devoid of risk, they could still be safer than synthetic drugs. Between 1968and 1997, the World Health Organization's monitoring center collected 8985 reports of adverse events associated with herbal medicines from 55 countries. Although this number may seem impressively high, it amounts to only a tiny fraction of adverse events associated with conventional drugs held in the same database." (BMJ, October 18, 2003; 327:881-882).

A meta-analysis published in the Journal of the American Medical Association(JAMA) reported the following: "The overall incidence of serious adverse drug reactions (ADRs) was 6.7% (95% confidence interval [CI], 5.2%-8.2%) and of fatal ADRs was 0.32% (95% CI, 0.23%-0.41%) of hospitalized patients. We estimated that in 1994overall 2,216,000 (1,721,000-2,711,000) hospitalized patients had serious ADRs and 106,000 (76,000-137,000) had fatal ADRs, making these reactions between the fourth and sixth leading cause of death." (JAMA. 1998;279:1200-1205)


  1. NIH Institute and Center Resources, National Institute of Health.

  2. More Than One-Third of U.S. Adults Use Complementary and Alternative Medicine, National Center for Complementary and Alternative Medicine Press release. May 27, 2004.

  • Herbs for serum cholesterol reduction: a systematic view, Thompson Coon JS and Ernst E. 2003 Jun

  • New England Journal of Medicineeditorial about the risks of alternative medicine

  • University of Marylandsite about alternative medicine: uses, possible prescription drug interactions, and possible nutrient depletions

  • Natural Products Discussion GroupInternet discussion group on the science and folklore of herbal medicines and natural productsde:Phytotherapie

  • Retrieved from "http://en.wikipedia.org/Herbalism"