Herbal, botanical, or phytomedicines are medicinal products containing active ingredients of exclusively plant origin.
These medicines may be consumed as comminuted powders or as decoctions.Their production may involve concentration or purification processes resulting in extracts, tinctures, fatty or essential oils, or expressed plant juices. This review of herbal medicines excludes products that consist primarily of chemically defined constituents. The demand for herbal remedies is rising in many countries. This resurgence in the use of medicinal herbs may be due to various reasons.
First, there is much disillusionment of the public with conventional medicine and its cost and inherent nonholistic approach. More important, there exists a perception among consumers that ‘‘natural’’ alternatives are safer than conventional medicine. In the United States, passage of the 1994 Dietary Supplementary Health and Education Act left the Food and Drug Administration (FDA) with limited jurisdiction over herbal products, resulting in a surge in the availability of herbal remedies to consumers. This may easily satisfy the consumers’ increasing desire for convenience and personal control over their own health. Also, the mass media, by providing reports.
of the ‘‘miraculous’’ healing effects of herbs, are fueling this trend, increasing the awareness of the consumer of the availability of various herbal remedy options. Since 1990, the U.S. market for herbal supplements has grown exponentially, to more than $2 billion a year in 1997, with no signs of leveling off. The U.S. herbal industry, now numbering more than 1300 companies, is expected to grow at a double-digit rate annually. In 1993 it was estimated that the Australians, too, were spending almost twice as much on complementary medicines (more than $600 million per year) as on pharmaceuticals. This trend is seen too not only in Europe but also in Asian countries. Singapore’s health care services are based mainly on Western medical science. However, with the development of traditional chinese medicine (TCM) particularly in China over the past two to three decades, and increasing interest in complementary medicine, Singapore’s public expenditure in TCM has also risen. TCM practice in Singapore is confined mainly to outpatient care. More than 10% of daily outpatient attendance is estimated to be seen by TCM practitioners, the majority of whom are trained locally by TCM schools.
The use of herbal medicines presents unique clinical and pharmacological challenges not encountered with conventional single-compound medicines. These medicines are usually complex mixtures of many bioactive compounds and conventional ‘‘indications and uses’’ criteria devised for single-compound entities may not be applicable in a significant number of ways. Compared to single-agent pharmaceuticals, phytomedicines may differ in the different mechanisms of action of bioactive constituents, in their doseresponse relationships, and in the synergistic/combinatorial effects of the many bioactive compounds in herbal extracts.
DIFFERENT MECHANISMS OF ACTION OF BIOACTIVE CONSTITUENTS
Observed effects may be the sum total of different classes of compounds having diverse mechanisms of action. The most widely used herbal medicine in Germany and Western countries is Gingko biloba. It is prescribed for ‘‘brain dysfunction’’ and to improve memory and cognition. In randomized placebo-controlled trials, the herb has been shown to improve memory impairment, cognitive performance, dementia, tinnitus, and intermittent claudication. The bioactive components of gingko are believed to include flavonoids and unique diterpenes called ginkolides. Gingkolides are potent inhibitors of the actions of platelet-activating factors, which are important for platelet activation and clotting. In addition, gingko extracts also exhibit antioxidation effects that are probably mediated through nitric oxide pathways. Thus platelet-activating and antioxidation effects could combine to reduce inflammation and increase microcirculatory blood flow and presumably improve brain function. This effect may also be augmented by the biflavone ginkgetin, which can downregulate COX-2 induction in vivo and this downregulating potential is associated with an antiinflammatory activity. These inflammatory effects are further augmented through the activation of other pathways by the ginkolides. For example, oral administration of the ginkolide bilobalide can protect against ischemia-induced neuron death by promoting expression of glial-cellline- derived neurotrophic factor and vascular endothelial growth factor in rat astrocytes. Other contributing effects are membrane-stabilizing, spasmolytic, and smooth-muscle-relaxation properties exerted through alpha-adrenergic receptors and the sympathetic nervous system. Thus many pathways may converge to give the total vasodilator and microvascular effects of gingko. Flavonoids are common compounds in plants with a role in the inhibition of interactions between plants and microbes. Soya products that contain flavonoids are thought to have potential health benefits in terms of cardiovascular health and postmenopausal symptoms and to prevent breast and prostate cancer. Genistein, one of the principal isoflavones in soy, has activity against the estrogen receptor and inhibits the tyrosine kinase receptor and DNA topoisomerase. It is also an antioxidant and affects the pathways of apoptosis. Ipriflavone, a synthetic isoflavone, was also shown to prevent bone loss through mechanisms that were different from the physiological estrogen (estradiol) in that it stimulated bone formation rather than suppressed bone resorption. Thus, whereas estradiol suppressed bone rate formation in ovariectomized rats, ipriflavone did not. Phytoestrogens also selectively activate the ER-beta more than the ER-alpha whereas the reverse is true for estradiol. Flavonoids are common in many herbal medicines including gingko and their myriad actions make analysis of outcome variables complicated.
PROBLEMS ASSOCIATED WITH THE USE OF HERBAL MEDICINES
Despite the popularity of botanical supplements, many herbal products on the market are of low quality and dubious efficacy. Scientists, clinicians, and consumers are often concerned about safety, effectiveness, and consistency of herbal preparations. Their apprehension about these qualities is due to a plurality of unknowns. These include a variety of poorly controlled factors such as raw herb quality, processing methods used to make the preparations, the complex biochemical heterogeneity of herbs, potential adulteration, unpredictable consequences when herbs are combined, unpredictable consequences when herbal remedies are combined with conventional medications,
and an apparent lack of scientific validation. It is not surprising that TCM, a medical paradigm that relies mainly on anecdotal data and tradition of use, frequently cannot withstand the scrutiny of evidence-based medicine.
Drug-herb Herb-Herb Interactions
Little more than anecdotal evidence exists regarding interactions between pharmaceutical and herbal medicines. Despite the widespread use of herbal medicines, documented herb-drug interactions are sparse. However, studies on the common herbs indicate that significant herb-drug interactions exists. Thus St. John’s wort (Hypericum perforatum) lowers blood concentrations of cyclosporin, amitriptyline, digoxin, indinavir, warfarin, phenprocoumon, and theophylline; furthermore, it causes intermenstrual bleeding, delirium, or mild serotonin syndrome, respectively, when used concomitantly with oral contraceptives (ethinylestradiol/desogestrel), loperamide, or selective serotonin-
reuptake inhibitors (sertaline, paroxetine, nefazodone). Ginkgo (Ginkgo biloba) interactions include bleeding when combined with warfarin, raised blood pressure when combined with a thiazide diuretic, and coma when combined with trazodone. Ginseng (Panax ginseng) lowers blood concentrations of alcohol and warfarin, and induces mania if used concomitantly with phenelzine. Garlic (Allium sativum) changes pharmacokinetic variables of paracetamol, decreases blood concentrations of warfarin, and produces hypoglycemia when taken with chlorpropamide. Kava (Piper methysticum) increases ‘‘off’’ periods in Parkinson patients taking levodopa and can cause a semicomatose state when given concomitantly with alprazolam. No interactions were found for echinacea (Echinacea angustifolia, E. purpurea, E. pallida) and saw palmetto (Serenoa repens). Thus, interactions between herbal medicines and synthetic drugs exist and can have serious clinical consequences.
Disclaimer: This website is for information purposes only. By providing the information contained herein we are not diagnosing, treating, curing, mitigating, or preventing any type of disease or medical condition. Before beginning any type of natural, integrative or conventional treatment regime, it is advisible to seek the advice of a licensed healthcare professional.
