Biological background
All plants produce chemical compounds as part of their normal metabolic activities. These include primary metabolites, such as sugars and fats, found in all plants, and secondary metabolites found in a smaller range of plants, some useful ones found only in a particular genus or species. Pigments harvest light, protect the organism from radiation and display colors to attract pollinators. Many common weeds have medicinal properties.[40][41]
The functions of secondary metabolites are varied. For example, some secondary metabolites are toxins used to deter predation, and others are pheromones used to attract insects for pollination. Phytoalexins protect against bacterial and fungal attacks. Allelochemicals inhibit rival plants that are competing for soil and light.
Plants upregulate and downregulate their biochemical paths in response to the local mix of herbivores, pollinators and microorganisms.[42] The chemical profile of a single plant may vary over time as it reacts to changing conditions. It is the secondary metabolites and pigments that can have therapeutic actions in humans and which can be refined to produce drugs.
Plants synthesize a bewildering variety of phytochemicals but most are derivatives of a few biochemical motifs.
- Alkaloids contain a ring with nitrogen. Many alkaloids have dramatic effects on the central nervous system. Caffeine is an alkaloid that provides a mild lift but the alkaloids in datura cause severe intoxication and even death.
- Phenolics contain phenol rings. The anthocyanins that give grapes their purple color, the isoflavones, the phytoestrogens from soy and the tannins that give tea its astringency are phenolics.
- Terpenoids are built up from terpene building blocks. Each terpene consists of two paired isoprenes. The names monoterpenes, sesquiterpenes, diterpenes and triterpenes are based on the number of isoprene units. The fragrance of rose and lavender is due to monoterpenes. The carotenoids produce the reds, yellows and oranges of pumpkin, corn and tomatoes.
- Glycosides consist of a glucose moiety attached to an aglycone. The aglycone is a molecule that is bioactive in its free form but inert until the glycoside bond is broken by water or enzymes. This mechanism allows the plant to defer the availability of the molecule to an appropriate time, similar to a safety lock on a gun. An example is the cyanoglycosides in cherry pits that release toxins only when bitten by a herbivore.
The word drug itself comes from the Dutch word "druug" (via the French word Drogue), which means 'dried plant'. Some examples are inulin from the roots of dahlias, quinine from the cinchona, morphine and codeine from the poppy, and digoxin from the foxglove.
The active ingredient in willow bark, once prescribed by Hippocrates, is salicin, which is converted in the body into salicylic acid. The discovery of salicylic acid would eventually lead to the development of the acetylated form acetylsalicylic acid, also known as "aspirin", when it was isolated from a plant known as meadowsweet. The word aspirin comes from an abbreviation of meadowsweet's Latin genus Spiraea, with an additional "A" at the beginning to acknowledge acetylation, and "in" was added at the end for easier pronunciation.[43] "Aspirin" was originally a brand name, and is still a protected trademark in some countries. This medication was patented by Bayer AG.
[edit] Herbal philosophy
Since herbalism is such a diverse field, few generalizations apply universally. Nevertheless a rough consensus can be inferred.
Most herbalists concede that pharmaceuticals are more effective in emergency situations where time is of the essence. An example would be where a patient had elevated blood pressure that posed imminent danger. However they claim that over the long term herbs can help the patient resist disease, and that in addition, they provide nutritional and immunological support that pharmaceuticals lack. They view their goal as prevention as well as cure.
Herbalists tend to use extracts from parts of plants, such as the roots or leaves but not isolate particular phytochemicals.[44] Pharmaceutical medicine prefers single ingredients on the grounds that dosage can be more easily quantified. Herbalists reject the notion of a single active ingredient. They argue that the different phytochemicals present in many herbs will interact to enhance the therapeutic effects of the herb and dilute toxicity.[45] Furthermore, they argue that a single ingredient may contribute to multiple effects. Herbalists deny that herbal synergism can be duplicated with synthetic chemicals. They argue that phytochemical interactions and trace components may alter the drug response in ways that cannot currently be replicated with a combination of a few putative active ingredients.[46][47] Pharmaceutical researchers recognize the concept of drug synergism but note that clinical trials may be used to investigate the efficacy of a particular herbal preparation, provided the formulation of that herb is consistent.[48]
In specific cases the claims of synergy[49] and multifunctionality[50] have been supported by science. The open question is how widely both can be generalized. Herbalists would argue that cases of synergy can be widely generalized, on the basis of their interpretation of evolutionary history, not necessarily shared by the pharmaceutical community. Plants are subject to similar selection pressures as humans and therefore they must develop resistance to threats such as radiation, reactive oxygen species and microbial attack in order to survive.[51] Optimal chemical defenses have been selected for and have thus developed over millions of years.[52] Human diseases are multifactorial and may be treated by consuming the chemical defences that they believe to be present in herbs. Bacteria, inflammation, nutrition and ROS (reactive oxygen species) may all play a role in arterial disease.[53] Herbalists claim a single herb may simultaneously address several of these factors. Likewise a factor such as ROS may underly more than one condition.[54] In short herbalists view their field as the study of a web of relationships rather than a quest for single cause and a single cure for a single condition.
In selecting herbal treatments herbalists may use forms of information that are not applicable to pharmacists. Because herbs can moonlight as vegetables, teas or spices they have a huge consumer base and large-scale epidemiological studies become feasible. Ethnobotanical studies are another source of information. [55] For example, when indigenous peoples from geographically dispersed areas use closely related herbs for the same purpose that is taken as supporting evidence for its efficacy.[citation needed] Herbalists contend that historical medical records and herbals are underutilized resources.[56] They favor the use of convergent information in assessing the medical value of plants. An example would be when in-vitro activity is consistent with traditional use.
Certain strains of herbalism rely on sources that would be widely considered unreliable and would not be accepted in a scientifically oriented herbal journal. These include astrology, the Bible, intuition, dreams, “plant spirits”, etc.
[edit] Popularity
A survey released in May 2004 by the National Center for Complementary and Alternative Medicine focused on who used complementary and alternative medicines (CAM), what was used, and why it was used. The survey was limited to adults, aged 18 years and over during 2002, living in the United States.
According to this survey, herbal therapy, or use of natural products other than vitamins and minerals, was the most commonly used CAM therapy (18.9%) when all use of prayer was excluded.[57][58]
Herbal remedies are very common in Europe. In Germany, herbal medications are dispensed by apothecaries (e.g., Apotheke). Prescription drugs are sold alongside essential oils, herbal extracts, or herbal teas. Herbal remedies are seen by some as a treatment to be preferred to chemical medications which have been industrially produced.[59]
In the United Kingdom, the training of medical herbalists is done by state funded Universities. For example, Bachelor of Science degrees in herbal medicine are offered at Universities such as University of East London, Middlesex University, University of Central Lancashire, University of Westminster, University of Lincoln and Napier University in Edinburgh at the present.
[edit] Types of herbal medicine systems
Use of medicinal plants can be as informal as, for example, culinary use or consumption of an herbal tea or supplement, although the sale of some herbs considered dangerous is often restricted to the public. Sometimes such herbs are provided to professional herbalists by specialist companies. Many herbalists, both professional and amateur, often grow or "wildcraft" their own herbs.
Some researchers trained in both western and traditional Chinese medicine have attempted to deconstruct ancient medical texts in the light of modern science. One idea is that the yin-yang balance, at least with regard to herbs, corresponds to the pro-oxidant and anti-oxidant balance. This interpretation is supported by several investigations of the ORAC ratings of various yin and yang herbs.[60][61]
Eclectic medicine came out of the vitalist tradition, similar to physiomedicalism and bridged the European and Native American traditions[citation needed]. Cherokee medicine tends to divide herbs into foods, medicines and toxins and to use seven plants in the treatment of disease, which is defined with both spiritual and physiological aspects, according to Cherokee herbalist David Winston.[62]
In India, Ayurvedic medicine has quite complex formulas with 30 or more ingredients, including a sizable number of ingredients that have undergone "alchemical processing", chosen to balance "Vata", "Pitta" or "Kapha."[63]
In addition there are more modern theories of herbal combination like William LeSassier's triune formula which combined Pythagorean imagery with Chinese medicine ideas and resulted in 9 herb formulas which supplemented, drained or neutrally nourished the main organ systems affected and three associated systems[citation needed]. His system has been taught to thousands of influential American herbalists through his own apprenticeship programs during his lifetime, the William LeSassier Archive[64] and the David Winston Center for Herbal Studies[65]
Many traditional African remedies have performed well in initial laboratory tests to ensure they are not toxic and in tests on animals. Gawo, a herb used in traditional treatments, has been tested in rats by researchers from Nigeria's University of Jos and the National Institute for Pharmaceutical Research and Development. According to research in the African Journal of Biotechnology, Gawo passed tests for toxicity and reduced induced fevers, diarrhoea and inflammation [66]
[edit] Routes of administration
The exact composition of a herbal product is influenced by the method of extraction. A tisane will be rich in polar components because water is a polar solvent. Oil on the other hand is a non-polar solvent and it will absorb non-polar compounds. Alcohol lies somewhere in between. There are many forms in which herbs can be administered, these include:
- Tinctures - Alcoholic extracts of herbs such as echinacea extract. Usually obtained by combining 100% pure ethanol (or a mixture of 100% ethanol with water) with the herb. A completed tincture has a ethanol percentage of at least 40-60% (sometimes up to 90%). [67]
- Herbal wine and elixirs - These are alcoholic extract of herbs; usually with an ethanol percentage of 12-38% [67] Herbal wine is a maceration of herbs in wine, while an elixir is a maceration of herbs in spirits (e.g., vodka, grappa, etc.)
- Tisanes - Hot water extracts of herb, such as chamomile.
- Decoctions - Long-term boiled extract of usually roots or bark.
- Macerates - Cold infusion of plants with high mucilage-content as sage, thyme, etc. Plants are chopped and added to cold water. They are then left to stand for 7 to 12 hours (depending on herb used). For most macerates 10 hours is used.[67]
- Vinegars - Prepared at the same way as tinctures, except using a solution of acetic acid as the solvent.
- Topicals:
- Essential oils - Application of essential oil extracts, usually diluted in a carrier oil (many essential oils can burn the skin or are simply too high dose used straight – diluting in olive oil or another food grade oil can allow these to be used safely as a topical).[68]
- Salves, oils, balms, creams and lotions - Most topical applications are oil extractions of herbs. Taking a food grade oil and soaking herbs in it for anywhere from weeks to months allows certain phytochemicals to be extracted into the oil. This oil can then be made into salves, creams, lotions, or simply used as an oil for topical application. Any massage oils, antibacterial salves and wound healing compounds are made this way.
- Poultices and compresses - One can also make a poultice or compress using whole herb (or the appropriate part of the plant) usually crushed or dried and re-hydrated with a small amount of water and then applied directly in a bandage, cloth or just as is.
- Whole herb consumption - This can occur in either dried form (herbal powder), or fresh juice, (fresh leaves and other plant parts).
- Syrups - Extracts of herbs made with syrup or honey. Sixty five parts of sugar are mixed with 35 parts of water and herb. The whole is then boiled and macerated for three weeks.[67]
- Extracts - Include liquid extracts, dry extracts and nebulisates. Liquid extracts are liquids with a lower ethanol percentage than tinctures. They can (and are usually) made by vacuum distilling tinctures. Dry extracts are extracts of plant material which are evaporated into a dry mass. They can then be further refined to a capsule or tablet. [67] A nebulisate is a dry extract created by freeze-drying.
- Inhalation as in aromatherapy can be used as a mood changing treatment[69][70] to fight a sinus infection or cough [71][citation needed], or to cleanse the skin on a deeper level (steam rather than direct inhalation here)[citation needed]
[edit] Examples of plants used as medicine
Few herbal remedies have conclusively demonstrated any positive effect on humans, mainly because of inadequate testing.[72] Many of the studies cited refer to animal model investigations or in-vitro assays and therefore cannot provide more than weak supportive evidence.
- Aloe vera has traditionally been used for the healing of burns and wounds.[73] A systematic review (from 1999) states that the efficacy of aloe vera in promoting wound healing is unclear, while a later review (from 2007) concludes that the cumulative evidence supports the use of aloe vera for the healing of first to second degree burns.[74][75]
- Agaricus blazei mushrooms may prevent some types of cancer.[76]
- Artichoke (Cynara cardunculus) may reduce production cholesterol levels according to in vitro studies [77] and a small clinical study.[78]
- Blackberry (Rubus fruticosus) leaf has drawn the attention of the cosmetology community because it interferes with the metalloproteinases that contribute to skin wrinkling.[79]
- Black raspberry (Rubus occidentalis) may have a role in preventing oral cancer.[80][81][82]
- Boophone (Boophone disticha) This highly toxic plant has been used in South African traditional medicine for treatment of mental illness [83]. Research demonstrate in vitro and in vivo effect against depression. [84][85][86]
- Butterbur (Petasites hybridus)
- Calendula (Calendula officinalis) has been used traditionally for abdominal cramps and constipation.[87] In animal research an aqueous-ethanol extract of Calendula officinalis flowers was shown to have both spasmolytic and spasmogenic effects, thus providing a scientific rationale for this traditional use.[88] There is "limited evidence" that calendula cream or ointment is effective in treating radiation dermatitis.[89][90]
- Cranberry (Vaccinium oxycoccos) may be effective in treating urinary tract infections in women with recurrent symptoms.[91]
- Echinacea (Echinacea angustifolia, Echinacea pallida, Echinacea purpurea) extracts may limit the length and severity of rhinovirus colds; however, the appropriate dosage levels, which might be higher than is available over-the-counter, require further research.[92][93]
- Elderberry (Sambucus nigra) may speed the recovery from type A and B influenza.[94] However it is possibly risky in the case of avian influenza because the immunostimulatory effects may aggravate the cytokine cascade.[95]
- Feverfew (Chrysanthemum parthenium) is sometimes used to treat migraine headaches.[96] Although many reviews of Feverfew studies show no or unclear efficacy, a more recent RTC showed favorable results[97][98][99] Feverfew is not recommended for pregnant women as it may be dangerous to the fetus.[100][101]
- Gawo (Faidherbia albida), a traditional herbal medicine in West Africa, has shown promise in animal tests [102]
- Garlic (Allium sativum) may lower total cholesterol levels[103]
- German Chamomile (Matricaria chamomilla) has demonstrated antispasmodic, anxiolytic, antiinflammatory and some antimutagenic and cholesterol-lowering effects in animal research.[104] In vitro chamomile has demonstrated moderate antimicrobial and antioxidant properties and significant antiplatelet activity, as well as preliminary results against cancer.[105][106] Essential oil of chamomile was shown to be a promising antiviral agent against herpes simplex virus type 2 (HSV-2) in vitro. [107]
- Ginger (Zingiber officinale), administered in 250 mg capsules for four days, effectively decreased nausea and vomiting of pregnancy in a human clinical trial.[108][109]
- Grapefruit (Naringenin) components may prevent obesity.
- Green tea (Camelia sinensis) components may inhibit growth of breast cancer cells[110] and may heal scars faster.[111]
- Purified extracts of the seeds of Hibiscus sabdariffa may have some antihypertensive, antifungal and antibacterial effect. Toxicity tested low except for an isolated case of damage to the testes of a rat after prolonged and excessive consumption.[112]
- Honey may reduce cholesterol.[113] May be useful in wound healing.[114]
- Lemon grass (Cymbopogon citratus), administered daily as an aqueous extract of the fresh leaf, has lowered total cholesterol and fasting plasma glucose levels in rats, as well as increasing HDL cholesterol levels. Lemon grass administration had no effect on triglyceride levels. [115]
- Magnolia
- Milk thistle (Silybum marianum) extracts have been recognized for many centuries as "liver tonics.".[116] Research suggests that milk thistle extracts both prevent and repair damage to the liver from toxic chemicals and medications.[117]
- Nigella sativa (Black cumin) has demonstrated analgesic properties in mice. The mechanism for this effect, however, is unclear. In vitro studies support antibacterial, antifungal, anticancer, anti-inflammatory and immune modulating effects.[118][119][120][121][122][123][124][125][126][127][128][129] However few randomized double blind studies have been published.
- Ocimum gratissimum[130][131] and tea tree oil can be used to treat acne.
- Oregano (Origanum vulgare) may be effective against multi-drug resistant bacteria.[132]
- Pawpaw can be used as insecticide (killing lice, worms).[133],[134]
- Peppermint oil may have benefits for individuals with irritable bowel syndrome.[135][136]
- Phytolacca or Pokeweed is used as a homeopathic remedy to treat many ailments. It can be applied topically or taken internally. Topical treatments have been used for acne and other ailments. It is used as a treatment for tonsilitis, swollen glands and weight loss.[citation needed]
- Pomegranate contains the highest percentage of ellagitannins of any commonly consumed juice. Punicalagin, an ellagitannin unique to pomegranate, is the highest molecular weight polyphenol known.[137] Ellagitannins are metabolized into urolithins by gut flora, and have been shown to inhibit cancer cell growth in mice.[138][139]
- Rauvolfia Serpentina, high risk of toxicity if improperly used[citation needed], used extensively in India for sleeplessness, anxiety, and high blood pressure.[140]
- Rooibos (Aspalathus linearis) contains a number of phenolic compounds, including flavanols, flavones, flavanones, flavonols, and dihydrochalcones.[141] Rooibos has traditionally been used for skin ailments, allergies, asthma and colic in infants.[142] In an animal study with diabetic mice, aspalathin, a rooibos constituent improved glucose homeostasis by stimulating insulin secretion in pancreatic beta cells and glucose uptake in muscle tissue.[143]
- Rose hips – Small scale studies indicate that hips from Rosa canina may provide benefits in the treatment of osteoarthritis.[144][145][146] Rose hips show anti COX activity.[147]
- Salvia lavandulaefolia may improve memory[148]
- Saw Palmetto can be used for BPH. Supported in some studies,[149] failed to confirm in others.[150]
- Shiitake mushrooms (Lentinus edodes) are edible mushrooms that have been reported to have health benefits, including cancer-preventing properties.[151] In laboratory research a shiitake extract has inhibited the growth of tumor cells through induction of apoptosis.[152] Both a water extract and fresh juice of shiitake have demonstrated antimicrobial activity against pathogenic bacteria and fungi in vitro.[153][154]
- Soy and other plants that contain phytoestrogens (plant molecules with estrogen activity) (black cohosh probably has serotonin activity) have some benefits for treatment of symptoms resulting from menopause.[155]
- St. John's wort, has yielded positive results, proving more effective than a placebo for the treatment of mild to moderate depression in some clinical trials[156] A subsequent, large, controlled trial, however, found St. John's wort to be no better than a placebo in treating depression[157] However, more recent trials have shown positive results[158][159][160] or positive trends that failed significance.[161] A 2004 meta-analysis concluded that the positive results can be explained by publication bias[162] but later analyses have been more favorable.[163][164] The Cochrane Database cautions that the data on St. John's wort for depression are conflicting and ambiguous.[165]
- Stinging nettle In some clinical studies effective for enign prostatic hyperplasia[166] and the pain associated with osteoarthritis.[167] In-vitro tests show antiinflammatory action.[168] In a rodent model, stinging nettle reduced LDL cholesterol and total cholesterol. [169] In another rodent study it reduced platelet aggregation.[170]
- Valerian root can be used to treat insomnia. Clinical studies show mixed results and researchers note that many trials are of poor quality.[171][172][173]
- Vanilla
[edit] Risks to health
In some cases, herbal medicines offer an inexpensive and safe alternative to pharmaceuticals. In the U.S., which has just 4% of the world's population, 106,000 patients died from and 2.2 million were seriously injured by adverse effects of pharmaceuticals in the year 1994 (Journal of the American Medical Association [2]).
Proper double-blind clinical trials are needed to determine the safety and efficacy of each plant before they can be recommended for medical use.[174] In addition, many consumers believe that herbal medicines are safe because they are natural. Herbal medicines may interact with synthetic drugs causing toxicity to the patient, herbal products may have contamination that is a safety consideration, and herbal medicines, without proven efficacy, may be used to replace medicines that have a proven efficacy.[72]
Standardization of purity and dosage is not mandated in the United States, but even products made to the same specification may differ as a result of biochemical variations within a species of plant.[175] Plants have chemical defense mechanisms against predators that can have adverse or lethal effects on humans. Examples of highly toxic herbs include poison hemlock and nightshade.[176] They are not marketed to the public as herbs, because the risks are well known, partly due to a long and colorful history in Europe, associated with "sorcery", "magic" and intrigue.[177] Although not frequent, adverse reactions have been reported for herbs in widespread use.[178] On occasion serious untoward outcomes have been linked to herb consumption. A case of major potassium depletion has been attributed to chronic licorice ingestion.[179] Black cohosh has been implicated in a case of liver failure.[180] Few studies are available on the safety of herbs for pregnant women.[181][182]
Herb drug interactions are a concern. In consultation with a physician, usage of herbal remedies should be clarified, as some herbal remedies have the potential to cause adverse drug interactions when used in combination with various prescription and over-the-counter pharmaceuticals.
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. Some herbs may amplify the effects of anticoagulants.[183] Certain herbs as well as common fruit interfere with cytochrome P450, an enzyme critical to drug metabolism.[184]
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