Medicinal plants
Medicinal plants, also called medicinal herbs, have been discovered and used in
The earliest historical records of herbs are found from the Sumerian civilization, where hundreds of medicinal plants including opium are listed on clay tablets, c. 3000 BC. The Ebers Papyrus from ancient Egypt, c. 1550 BC, describes over 850 plant medicines. The Greek physician Dioscorides, who worked in the Roman army, documented over 1000 recipes for medicines using over 600 medicinal plants in De materia medica, c. 60 AD; this formed the basis of pharmacopoeias for some 1500 years. Drug research sometimes makes use of ethnobotany to search for pharmacologically active substances, and this approach has yielded hundreds of useful compounds. These include the common drugs aspirin, digoxin, quinine, and opium. The compounds found in plants are diverse, with most in four biochemical classes: alkaloids, glycosides, polyphenols, and terpenes. Few of these are scientifically confirmed as medicines or used in conventional medicine.
Medicinal plants are widely used as folk medicine in non-industrialized societies, mainly because they are readily available and cheaper than modern medicines. The annual global export value of the thousands of types of plants with medicinal properties was estimated to be US$60 billion per year and growing at the rate of 6% per annum.[citation needed] In many countries, there is little regulation of traditional medicine, but the World Health Organization coordinates a network to encourage safe and rational use. The botanical herbal market has been criticized for being poorly regulated and containing placebo and pseudoscience products with no scientific research to support their medical claims.[3] Medicinal plants face both general threats, such as climate change and habitat destruction, and the specific threat of over-collection to meet market demand.[3]
History
Prehistoric times
Plants, including many now used as
Ancient times
In ancient
From ancient times to the present,
Middle Ages
In the
Early Modern
The
19th and 20th centuries
The place of plants in medicine was radically altered in the 19th century by the application of
Context
Medicinal plants are used with the intention of maintaining health, to be administered for a specific condition, or both, whether in modern medicine or in traditional medicine.[3][36] The Food and Agriculture Organization estimated in 2002 that over 50,000 medicinal plants are used across the world.[37] The Royal Botanic Gardens, Kew more conservatively estimated in 2016 that 17,810 plant species have a medicinal use, out of some 30,000 plants for which a use of any kind is documented.[38]
In modern medicine, around a quarter[a] of the drugs prescribed to patients are derived from medicinal plants, and they are rigorously tested.[36][39] In other systems of medicine, medicinal plants may constitute the majority of what are often informal attempted treatments, not tested scientifically.[40] The World Health Organization estimates, without reliable data, that some 80 percent of the world's population depends mainly on traditional medicine (including but not limited to plants); perhaps some two billion people are largely reliant on medicinal plants.[36][39] The use of plant-based materials including herbal or natural health products with supposed health benefits, is increasing in developed countries.[41] This brings attendant risks of toxicity and other effects on human health, despite the safe image of herbal remedies.[41] Herbal medicines have been in use since long before modern medicine existed; there was and often still is little or no knowledge of the pharmacological basis of their actions, if any, or of their safety. The World Health Organization formulated a policy on traditional medicine in 1991, and since then has published guidelines for them, with a series of monographs on widely used herbal medicines.[42][43]
Medicinal plants may provide three main kinds of benefit: health benefits to the people who consume them as medicines; financial benefits to people who harvest, process, and distribute them for sale; and society-wide benefits, such as job opportunities, taxation income, and a healthier labour force.[36] However, development of plants or extracts having potential medicinal uses is blunted by weak scientific evidence, poor practices in the process of drug development, and insufficient financing.[3]
Phytochemical basis
All plants produce chemical compounds which give them an
Modern knowledge of medicinal plants is being systematised in the Medicinal Plant Transcriptomics Database, which by 2011 provided a sequence reference for the transcriptome of some thirty species.[49] Major classes of plant phytochemicals are described below, with examples of plants that contain them.[8][43][50][51][52]
Alkaloids
-
The alkaloid nicotine from tobacco binds directly to the body's Nicotinic acetylcholine receptors, accounting for its pharmacological effects.[58]
-
Deadly nightshade, Atropa belladonna, yields tropane alkaloids including atropine, scopolamine and hyoscyamine.[54]
Glycosides
The
-
Thefoxglove, Digitalis purpurea, contains digoxin, a cardiac glycoside. The plant was used on heart conditions long before the glycoside was identified.[44][63]
Polyphenols
Many polyphenolic extracts, such as from
-
Angelica, containing phytoestrogens, has long been used for gynaecological disorders.
Terpenes
-
Theantifungal.[76]
In practice
Cultivation
Medicinal plants demand intensive management. Different species each require their own distinct conditions of cultivation. The World Health Organization recommends the use of rotation to minimise problems with pests and plant diseases. Cultivation may be traditional or may make use of conservation agriculture practices to maintain organic matter in the soil and to conserve water, for example with no-till farming systems.[77] In many medicinal and aromatic plants, plant characteristics vary widely with soil type and cropping strategy, so care is required to obtain satisfactory yields.[78]
Preparation
Medicinal plants are often tough and fibrous, requiring some form of preparation to make them convenient to administer. According to the Institute for Traditional Medicine, common methods for the preparation of herbal medicines include decoction, powdering, and extraction with alcohol, in each case yielding a mixture of substances. Decoction involves crushing and then boiling the plant material in water to produce a liquid extract that can be taken orally or applied topically.[79] Powdering involves drying the plant material and then crushing it to yield a powder that can be compressed into tablets. Alcohol extraction involves soaking the plant material in cold wine or distilled spirit to form a tincture.[80]
Traditional poultices were made by boiling medicinal plants, wrapping them in a cloth, and applying the resulting parcel externally to the affected part of the body.[81]
When modern medicine has identified a drug in a medicinal plant, commercial quantities of the drug may either be synthesised or extracted from plant material, yielding a pure chemical.[33] Extraction can be practical when the compound in question is complex.[82]
Usage
Plant medicines are in wide use around the world.
Drugs derived from plants including opiates, cocaine and cannabis have both medical and
Effectiveness
Plant medicines have often not been tested systematically, but have come into use informally over the centuries. By 2007, clinical trials had demonstrated potentially useful activity in nearly 16% of herbal extracts; there was limited in vitro or in vivo evidence for roughly half the extracts; there was only phytochemical evidence for around 20%; 0.5% were allergenic or toxic; and some 12% had basically never been studied scientifically.[43] Cancer Research UK caution that there is no reliable evidence for the effectiveness of herbal remedies for cancer.[91]
A 2012
Regulation
The World Health Organization (WHO) has been coordinating a network called the International Regulatory Cooperation for Herbal Medicines to try to improve the quality of medical products made from medicinal plants and the claims made for them.
WHO has set out a strategy for traditional medicines[95] with four objectives: to integrate them as policy into national healthcare systems; to provide knowledge and guidance on their safety, efficacy, and quality; to increase their availability and affordability; and to promote their rational, therapeutically sound usage.[95] WHO notes in the strategy that countries are experiencing seven challenges to such implementation, namely in developing and enforcing policy; in integration; in safety and quality, especially in assessment of products and qualification of practitioners; in controlling advertising; in research and development; in education and training; and in the sharing of information.[95]
Drug discovery
The
Hundreds of compounds have been identified using
The pharmaceutical industry has remained interested in mining traditional uses of medicinal plants in its drug discovery efforts.[33] Of the 1073 small-molecule drugs approved in the period 1981 to 2010, over half were either directly derived from or inspired by natural substances.[33][102] Among cancer treatments, of 185 small-molecule drugs approved in the period from 1981 to 2019, 65% were derived from or inspired by natural substances.[103]
Safety
Plant medicines can cause adverse effects and even death, whether by side-effects of their active substances, by adulteration or contamination, by overdose, or by inappropriate prescription. Many such effects are known, while others remain to be explored scientifically. There is no reason to presume that because a product comes from nature it must be safe: the existence of powerful natural poisons like atropine and nicotine shows this to be untrue. Further, the high standards applied to conventional medicines do not always apply to plant medicines, and dose can vary widely depending on the growth conditions of plants: older plants may be much more toxic than young ones, for instance.[105][106][107][108][109][110]
Plant extracts may interact with conventional drugs, both because they may provide an increased dose of similar compounds, and because some phytochemicals interfere with the body's systems that metabolise drugs in the liver including the cytochrome P450 system, making the drugs last longer in the body and have a cumulative effect.[111] Plant medicines can be dangerous during pregnancy.[112] Since plants may contain many different substances, plant extracts may have complex effects on the human body.[5]
Quality, advertising, and labelling
Herbal medicine and
Threats
Where medicinal plants are harvested from the wild rather than cultivated, they are subject to both general and specific threats. General threats include climate change and habitat loss to development and agriculture. A specific threat is over-collection to meet rising demand for medicines.[121] A case in point was the pressure on wild populations of the Pacific yew soon after news of taxol's effectiveness became public.[33] The threat from over-collection could be addressed by cultivation of some medicinal plants, or by a system of certification to make wild harvesting sustainable.[121] A report in 2020 by the Royal Botanic Gardens, Kew identifies 723 medicinal plants as being at risk of extinction, caused partly by over-collection.[122][103]
See also
- Australian Phytochemical Survey
- Ethnomedicine
- European Directive on Traditional Herbal Medicinal Products
- Plant Resources of Tropical Africa
Notes
- ^ Farnsworth states that this figure was based on prescriptions from American community pharmacies between 1959 and 1980.[39]
- ^ Berberine is the main active component of an ancient Chinese herb Coptis chinensis French, which has been administered for what Yin and colleagues state is "diabetes" for thousands of years, although with no sound evidence of efficacy.[55]
- ^ Tobacco has "probably been responsible for more deaths than any other herb", but it was used as a medicine in the societies encountered by Columbus and was considered a panacea in Europe. It is no longer accepted as medicinal.[56]
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