Written by Simon Mills
Modern expectations for medicines are that they should have been thoroughly tested to make sure that they work and are safe. Doctors and health regulators use the term ‘evidence-based medicine’ (EBM) as their default for approving treatments. Although this principle does not always apply in medical practice, many say that herbal remedies have not met these standards and should not be recommended. Here we will address that charge and argue that the appropriate use of herbs is fully justified.
The ‘gold standard’ measure of efficacy is the randomised double-blind controlled clinical trial (RCT). The remedy to be tested is given to a population of subjects on the same basis as a placebo or comparison medicine in a way that neither the subjects nor the investigators know who is getting which. This is intended to reduce conscious and unconscious bias, and by careful matching of each comparison group, and choosing a large enough population, to eliminate other factors such as natural improvements in the condition, suggestion and expectations, that may affect outcome.
There are many arguments about the reliability of the RCT to all circumstances and conditions. It does not reflect individual experiences of illness, is less useful in complex, rare and long-term conditions and blinding is often hard to assure. ‘Publication bias’ results when authors and sponsors hold back on results that do not reflect their expectations and tends to skew reports towards those that are positive. RCTs are very demanding and methodological rigour is also not assured. Nevertheless there is no substitute for a good RCT if we want to get some measure of the independent activity of a remedy.
RCTs require complex organisational capacity, specialist statistical and other skills, are subject to intensive ethical scrutiny, and therefore are notoriously expensive. However there are increasing numbers of such studies being published for herbs. For many on this site (those that have been updated and have the ‘New’ tag) we have attached an Expert Herbal Reality Resource. Do take a look at the Evidence section in these pdfs and you will see a significant number of RCTs, most of which have been published in the last few years. So this evidence base is certain to grow.
There is no doubt however that the RCT inventory for herbs is patchy and usually not conclusive. The best way to consider the evidence base is to link it to the most substantial resource we do have: the many centuries of human experience.
The evidence of experience
We can claim really useful information by distilling out the vast store of historical and anthropological records for the use of herbs as medicines (the science of ethnopharmacology). We can note that there would have been little room for sentiment and idealism in the life-and-death situations that prevailed through most of history. The herbal remedies that have floated to the top of popular reputation around the world will have been tried and tested in the most adverse conditions, as the only medicines available and without backup ambulances and hospital emergency rooms: if they did not work they would not have been continuously and widely used.
However without rigorous screening the record of traditional use can appear motley. Each community and even family will have its own favourites. The placebo effect of a cultural icon is very powerful: if everyone around you is convinced that the remedy will work then it likely will. Assessing traditional reputations is only reliable if we take broad overviews of the multitude of local stories.
Fortunately we can do this. We can take anthropological records from around the world. We can discount one tradition as a local fashion; if we can find a similar use in two discrete locations that looks like something more substantial; three or more distinct uses becomes a much stronger lead. Some of our most popular remedies like green tea, licorice, chamomile, dandelion, mint, ginger, turmeric, cinnamon and other spices have all established global reputations by being rediscovered anew in many parts of the world. Some of the regional high flyers, for example: andrographis, ashwagandha, gotu kola, shatavari from India; astragalus, ginseng from China; echinacea from North America, have grown their reputation across many distinct regions in their own continents and have established themselves more widely as well. We can also go deeper and look at what emerge as universal core pharmaceutical principles of early medicine, applying the simplest of all technologies: taste, smell and other senses.
The pharmacology of experience: the science of traditional medicine
When animals encounter plants they use their senses to understand them. Taste and smell are the main judges of quality and safety. Humans inherited these same instincts and then elaborated them to construct basic pharmaceutical standards for evaluating their remedies.
All classical medical traditions, from India, China, Islam and Europe categorised their medicines by taste and sensory quality. Although the language and cultural meanings were different the core insights were astonishing consistent and we can distil simple principles that each of us can use today.
If you look at the descriptions of the herbs on this site you will see that we invite you to do what our ancestors did: taste the herb! This is often a striking revelation. From what is often a powerful simple sensory hit we can often feel for ourselves what our elders understood about these remedies.
The impact of the senses
The following presents commonly encountered impacts of herbal remedies and how they translate into modern descriptions of their effects when we consume them. Key phytochemical groups are in bold: these most clearly transfer sensory experiences into pharmacology and are like the Rosetta stone – they provide instant translation of multiple local traditions into modern language.
An ‘aromatic’ remedy, high in volatile essential oils, was most often associated with calming and sometimes ‘warming’ the digestion. Most kitchen spices and herbs have this quality: they were used both as flavouring and to ease the digestion of sometimes challenging pre-industrial foods. Many aromatics are classed as ‘carminatives’ and are used to reduce colic, bloating and agitated digestion.
They also often feature in respiratory remedies for colds, chest and other airway infections. They are also classic calming inhalants and massage oils, and are the basis of aromatherapy for their mental benefits.
The puckering taste you get with many plants (the most familiar is black tea after being stewed too long, or some red wines) is produced by complex polyphenols such as tannins. Tannins are used in concentrated form (eg from oak bark) to make leather from animal skins. The process of ‘tanning’ involves the coagulation of relatively fluid proteins in living tissues into tight clotted fibres (similar to the process of boiling an egg). Tannins in effect turn exposed surfaces on the body into leather. In the case of the lining of mouth and upper digestive tract this is only temporary as new mucosa are replenished, but in the meantime can calm inflamed or irritated surfaces. In the case of open wounds tannins can be a life-saver – when strong (as in the bark of broadleaved trees like oak) they can seal a damaged surface.
One group of tannins, the reddish-brown ‘condensed tannins’ are classified as procyanidins, which can reduce inflammation and oxidative damage.
Bitters are a very complex group of phytochemicals with one thing in common: they stimulate the bitter receptors in the mouth. They were some of the most valuable remedies in ancient medicine. They were experienced as stimulating appetite and switching on a wide range of key digestive functions, including increasing bile clearance from the liver (as bile is a key factor in bowel health this can now be translated into improving bowel functions and the microbiome). Many of these reputations are being supported by new research on the role of bitter receptors in the mouth and elsewhere round the body.
Bitters were also seen as ‘cooling’ reducing the intensity of some fevers and inflammatory diseases.
Any fruits with a blue-purple colouring contain high levels of the polyphenols known as anthocyanidins. These work 1) on the walls of small blood vessels, helping to maintain capillary structure to reduce a key stage in inflammation, and improving the microcirculation to the tissues; 2) to improve retinal function and vision; 3) to support connective tissue repair around the body.
Traditional ‘hot’ or ‘heating’ remedies, often containing spice ingredients like capsaicin, the gingerols (ginger), piperine (black or long pepper), curcumin (turmeric) or the sulfurous isothiocyanates from mustard, horseradich or wasabi, generate warmth when taken. In modern times this might translate as thermogenic and circulatory stimulant effects. There is evidence of improved tissue blood flow with such remedies: this would lead to a reduction in build-up of metabolites and tissue damage.
Heating remedies were used to counter the impact of cold, reducing any symptoms made worse in the cold. The proof of this effect is in the doing of it: the results are often almost immediate!
Mucilages are complex carbohydrate based plant constituents with a slimy or ‘unctuous’ feel especially when chewed or macerated in water. Their effect is due simply to their physical coating exposed surfaces. From prehistory they were most often used as wound remedies for their soothing and healing effects on damaged tissues. Nowadays they are used more for these effects on the digestive lining, from the throat to the stomach, where they can relieve irritation and inflammation such as pharyngitis and gastritis. Some of the prominent mucilaginous remedies like slippery elm, aloe vera and the seaweeds can be used as physical buffers to reduce the harm and pain caused by reflux of excess stomach acid.
Mucilages are also widely used to reduce dry coughing. Here the effect seems to be by reflex through embryonic nerve connections: reduced signals from the upper digestive wall appear to translate as reduced activity of airway muscles and increased activity of airway mucus cells. Some seed mucilages, such as in psyllium seed, flaxseed (linseed) or guar bean survive digestion to provide bulking laxative effects in the bowel. These can also reduce rate of absorption of sugar and cholesterol
Resins are most familiar as tacky discharges from pine trees (and as the substance in amber, and rosin for violin bows). They were most valued however as the basis of ancient commodities like frankincense and myrrh (two of the three gifts of the Three Wise Men to the baby Jesus) and getting access to their source was one benefit to Solomon for marrying the Queen of Sheba (now Ethiopia). Resins were the original antiseptic remedies, ground and applied as powders or pastes to wounds or inflamed tissues, and were also used for mummification.
With alcohol distillation it was found that they could be dissolved in 90% alcohol and in this form they remain a most powerful mouthwash and gargle, for infected sore throats and gum disease. They never attracted much early research interest because they permanently coat and damage expensive glassware! For use in the mouth, gums and throat they are best combined with concentrated licorice extracts to keep the resins in suspension and add extra soothing properties. It appears that they work both as local antiseptics and by stimulating white blood cell activity under the mucosal surface. They feel extremely effective!
The sharp taste of some fruits, and almost all unripe fruits, as well as vinegar and fermented foods, is produced by weak acids (the taste is generated by H+ ions from acids stimulating the sour taste buds). Sour taste buds are hard-wired to generate immediate reflex responses elsewhere in the body. Anyone who likes the refreshing taste of lemon or other citrus in the morning will know that one reflex effect is increased saliva production.
Other effects are subjective rather than confirmed by research but there is a consistent view that they include increased digestive activity and contraction of the gallbladder.
Smell of hay
The familiar country odour of haymaking, of drying grass and other plants, is largely produced by coumarins (originally isolated from tonka beans – in French coumarou) and widely used in perfumery. They have strong antioxidant activity in the laboratory and likely effects in modulating inflammation. They were most often associated with plants used in stuffing mattresses and pillows to encourage sleep.
When extracted in water some plants cause a lather and are used for washing. This property is due to the presence of saponins (from the Latin for soap), which are plant steroids. Plants that are rich in saponins keep appearing across the world as important gynaecological and adaptogenic remedies (examples are shatavari, ashwagandha, astragalus, brahmi, ginseng, eleutherococcus, licorice, kava, wild yam, and several important Native North American women’s remedies). Given this striking association it has been speculated that these plant steroids may modulate steroids metabolism in the adrenal cortex, ovary, and testes. Saponins are discussed briefly in a similar context under the sweet taste below.
Other saponins are used for their detergent properties as cough remedies: examples are the primulas, soapwort, senega, and ivy leaf. These exert a minor irritant effect similar to that of emetics and induce a well-known expectorant response by reflex from the upper gut to the airways.
In the days when most people never tasted sugar, ‘sweetness’ was associated with the taste of basic foods: that of cooked vegetables, cereals and meat. In other words sweet was the quality of nourishment, and ‘tonic’ remedies. Describing a remedy as sweet generally led to that remedy being used in convalescence or recovery from illness.
Interestingly, the plant constituents most often found in classic tonics like licorice, ginseng are plant steroids including saponins, which also have a sweet taste.
A different understanding of medicine
A key point about these sensory guides to the action of herbs is that they led to a quite different understanding of what a medicine does. In herbal tradition medicines were classified by what they did for the body rather than what diseases you used them for. Medicines were warming or cooling, drying or moistening; they moved variously through the body, they aided eliminations from various quarters, they tonified. The aim in herbal treatment is to match the action of the medicine to the needs of each individual. It is critical in understanding the traditional evidence base to understand this distinction and to incorporate it into any practice-based judgment.
Modern endorsement of traditional use
Even however taking a modern medical view, there are many other cases where scientific research can illuminate and validate traditional practices, and vice versa. The early use of salicylate-rich willow bark to reduce fever and inflammation, the widespread use of licorice sticks as tooth brushes, the 3000-year use of psoralen-rich plants in the treatment of vitiligo in India, the use in ancient Egypt of a treatment for angina pectoris based on visnagin and khellin, the unusual traditional practices in the growth and preparation of kava for reducing anxiety: all have all been validated by modern research and lessons have been learnt. Ethnopharmacological studies show countless examples where pharmacological activity can be demonstrated in traditional remedies and practices.
Such tie-ups are clearly interesting; in effect the early reputation provides “human bioassay data” as a basis for future research and an assurance of relative safety. By contrast modern medicinal research has to start with novel chemicals that have never been used by humans before, and most promising new leads fail for safety reasons.
The examples above suggest that being able to combine two or more incomplete data sources can provide useful pointers to benefit, especially as the calculations are bedded in longterm human use over centuries.
All such evidence is circumstantial until fully verified. However if you are looking for promising leads to help someone whose conditions are not otherwise being well managed, then you can do worse than apply that other law-court principle, “on the balance of probabilities”, and try out one of the established traditional herbal remedies described on this site.
- Evidence-base for herbal practice
There are many robust sources of herbal evidence, with online libraries like PubMed (free), Embase and Scopus (subscription) providing updated clinical trial reports, systematic reviews and meta-analyses in real time. There are also a range of paid-for herb-specific literature review services such as ESCOP, Natural Standard, HerbMedPro, the American Herbal Pharmacopeia and other specialist services.
The following texts are useful resources for practitioners wishing to use the evidence base in support of their clinical application of herbal remedies:
- Barnes, J, Anderson L, Phillipson JD (2007) Herbal Medicines 3rd Edition. Pharmaceutical Press, London [leading pharmacy-oriented guide to the evidence]
- Bone K and Mills S (2013) Principles and Practice of Phytotherapy, 2nd Edition. Churchill Livingstone/Elsevier. [standard evidence-based text used in herbal medicine courses]
- Mills, S and Bone K eds (2005) The Essential Guide to Herbal Safety. Churchill Livingstone/Elsevier [a pragmatic guide to real and imagined safety evidence]
Rigorous consensus reviews of efficacy and safety evidence for many herbs used in Europe as medicines are available free online from The European Medicines Agency
2. Traditional use information
There are few original resources for those starting out on a search of traditional uses of herbal remdies. The following are recommended as including original anthropological accounts of traditional use. The focus here is on how earlier traditions were articulated in modern times, particularly the 19th and 20th centuries, rather than going to pre-modern original texts. Serious scholars will go to major resources like the Wellcome Library for the History of Medicine in London, or pursue ethnopharmacological literature at various schools of pharmacy and universities around the world.
These texts are suggested as introductions to traditional use of plants in different cultures.
- British Herbal Medicine Association. (1983) The British Herbal Pharmacopoeia 1983. Bournemouth, England. [UK herbal practitioner practices up to the mid-20th century]
- Dalby, A (2000) Dangerous tastes: the story of spices.British Museum Press, London. [fascinating story of the world spice traditions and trading histories]
- Kaptchuk, T.J. (1983) The Web that has no Weaver: Understanding Chinese Medicine. Congdon & Weed, New York. [the most accessible introduction to the therapeutic principles]
- Lassak EV. and McCarthy T. (1983) Australian Medicinal Plants. Methuen Australia
- MacDonald, C (1974) Medicines of the Maori. Collins, New Zealand. [a great example of traditional use uninfluenced by other cultures]
- Moerman D.E. (1998) Native American Ethnobotany. Timber Press, Portland, Oregon [the most comprehensive resource of indigenous North American tribal uses]
- Perry L.R. (1980) Medicinal Plants of East and Southeast Asia. The Massachusetts Institute of Technology Press. [an absolute classic resource of Asian folk use]
- Pole, S (2013). Ayurvedic Medicine. Elsevier [a great modern review of this tradition for the modern world]
- Ullman, M. (1978) Islamic Medicine. Edinburgh University Press
- Unschuld, P.U. (1985) Medicine in China: A history of Ideas. University of California Press. [a masterful review of the context]
- Vogel V.J. (1970) American Indian Medicine. University of Oklahoma Press. [a classic review]