Medicinal Plant Constituents and Actions

A summary of some important medicinal plant constituents and examples of herbs they are found in.

Medicinal plants are very much the backbone for modern allopathic medicine. The array of important medicinal plant constituents are listed here, in no particular order.

In general, the more atoms a molecule has, the heavier it is. Simple, carbon-based molecules we use every day, include the range of extremely volatile hydro-carbon fuels such as methane, butane, propane (1, 3 and 4 carbon atoms respectively), octane (8 atoms), as well as the multitude of aromatic and volatile components in plant essential oils (generally having 10 or 15 carbon atoms), utilised in cookery and herbal medicine.

Monobasic acids including aliphatic (straight chain) acids

Containing up to 26 carbon atoms per molecule, these include formic acid, acetic acid and a range of saturated and unsaturated fatty acids as well as valeric acid from hops and valerian.


Polybasic acids

Containing more than one carboxylic group, very widely found in plants. Noted for slight laxative action and include oxalic, succinic and fumaic acids.


Hydroxy acids

These include both a pair of –COOH (acid) groups together with an –OH group (alcohol, or hydroxyl group). This gives them properties of alcohols as well as acids. These include citric, malic, and tartaric acids. The presence of hydroxyl groups provides reactive sites on a molecule.

Citric acid

This acid appears widely in fruit and berries, especially the citrus fruits. It plays a key role in metabolism. It is classed as an alkaline food source because it breaks down to bicarbonates in the stomach. It is a gentle osmotic (water-attracting) laxative and diuretic.


Oxalic acid

A common plant constituent, and widely found in the dock family. It can also be found in the tea plant, spinach and parsley amongst others. It forms insoluble salts with metals such as calcium and is often found in this form. This substance imparts a distinctive lemony or citrus taste to plant leaves.

One potential problem from over excessive consumption of oxalates is the formation of urinary stones. These are produced by precipitation of excessive oxalates in acid urine. Another consequence is gout, whereby skeletal joints accumulate large amounts of these crystal deposits, bringing regular and extreme discomfort to sufferers.


Un-saturated fatty acids

Certain fatty acids are vital for life. Hence the term essential fatty acid. Our bodies require them to build and repair cell walls, cell membranes, and C.N.S tissues. Inflammation and other chronic diseases have been documented in people exhibiting a deficiency of polyunsaturated acids in the blood.

These fatty acids are universally found in plants. Notable examples include linolenic acid (found mainly in growing green tissues) and arachidonic acid (found mostly in seeds and other reproductive tissues). Certain hormones involved in inflammatory responses, collectively known as prostaglandins (Pg’s), are made from arachidonic acid.

Carbohydrates (CHO’s)

These are built from basic units (sugars) and can be classified as to the number of sugars they contain. CHOs are a collective term for molecules comprised of carbon, hydrogen and oxygen and are similar to hydrocarbon fuels we use to power our cars.

All sugars are CHOs and they come in all manner of guises, i.e. with differing numbers of carbon atoms. For example, Glucose sugar has six carbon atoms, whereas sucrose, (more commonly known as granulated sugar) is comprised of two glucose molecules joined together, and contains 12 carbon atoms.

The vast number of polysaccharides present in plants including starch and inulin, have much longer chains of glucose molecules, and these take longer to breakdown in the body, hence their value as a long-term energy source.

Hydrocarbon vehicle fuels do not contain oxygen and burn brighter and faster than CHOs. Basically, CHOs do pretty much the same job and are by far the major basic source of fuel for the human body. As with the performance differences between fuels such as petrol or octane, the differences in the long chain sugar molecules that we consume (and there are many different types) will have resultant dramatic performance differences within the body.

All sugars end in the suffix –ose as in glucose and fructose. All enzymes (protein-based, metabolic, catalysing co-factors made from amino-acids) end in the suffix –ase, as in the starch-digesting saliva enzyme amylase. Acid substances are given the suffix –ates, so wherever you see this molecule name ending you know you are dealing with an acid, as in salicylates (salicylic acid) folate (folic acid), pyruvate etc.

Monosaccharides (mono = one, saccharide = sugar)

Also known as simple sugars. Examples are fructose, glucose, galactose, and the wood sugars xylose, ribose, and arabinose. Apiose from celery is another example.

Disaccharides (Di = two)

Molecules containing two sugar units. They include sucrose (glucose and fructose combined), maltose (glucose x 2) and lactose (galactose and glucose), which is found in milk only. They are quickly broken down by the body to mono-saccharides, although several, such as raffinose, are reputed to contribute to the undigested CHO residue we call ‘roughage’.

Polysaccharides (Poly = many)

These are often rather large molecules. Included here are the amyloses that constitute the glucose storage molecules such as starch, glycogen, cellulose, and inulin (a fructose-based storage substance), commonly found in the daisy family.

Inula helenium, has huge rhizomes full of inulin and essential oils

Plants containing them include the jerusalem artichoke (Helianthus tuberosum), elecampagne (Inula helenium), and dandelion. Other polysaccharides include molecules that contain other components beside sugar units, such as hemi-celluloses, pectins, gums, and mucilages.

Gums and mucilages (G&M’s)

Very common plant constituents, they are chemically similar,

Allantoin, an important and common medicinal plant constituent

 yet traditionally distinguished by their physical properties – a gum being tacky, a mucilage slimy. The actions of G&M’s are more physical than chemical.

They are made from uronic acid and sugar derivatives, and even if broken down on digestion have little pharmacological effect. Mostly these molecules are resistant to digestive juices and many survive to reach the bowel.

Comfrey species are rich in allantoin, an important medicinal plant constituent
Comfrey (Symphytum officinale) contains a high amount of the mucilage rich compound allantoin

Yet plants containing G&M’s such as marshmallow (Althaea officinalis), comfrey, plantains, slippery elm bark (Ulmus fulva), and coltsfoot all benefit the digestive system, respiratory system and urinary system.

Whilst no useful parts of the mucilage’s reach those parts of the body, the proposed overall effects point to the relationship between the origins of these three bodily systems. During embryonic development of the body, due to the bronchial tree and urinary tissues developing as an offshoot of the gut, the tissues of these systems have a common source.

Therefore, agents that affect the lining and wall of the digestive tract will, by nerve-ending reflex action, influence the function of the bronchial and urinary ducts. Mucilages readily produce a slimy coating which soothes and protects any exposed mucosal surface.

For this reason, plants containing mucilage’s are primarily used as wound remedies, helping to soothe pain, irritation, and itching, and as they dry they often bind to any damaged tissue.

The plantains contain mucilage when crushed, and are demulcent herbs to soothe wounds

The actions shown by mucilages are classed as emollient or demulcent. Mucilaginous remedies are proven as invaluable in treating digestive disorders. They soothe irritation that can be behind a range of symptoms such as flatulence, colic, dyspepsia, spastic bowel, vomiting and diarrhoea as well as many cases of abdominal pain.

This demulcent action continues along the digestive tract lining, which helps explain the use of mucilaginous remedies for gastro-intestinal inflammations, ulcers, lesions, as well as for reducing irritant results of excessive stomach acid or digestive juice secretion.

Immune system stimulating polysaccharides- The fizzy medicinal plant constituents

These are water-soluble, acidic, branch-chained polysaccharides with high molecular weights. Similar molecularly to the sugary sweets that fizz on your tongue, these medicinal plant constituents exhibit significant immuno-stimulating properties.

Medicinal plants showing these actions include the three species of Echinacea commonly used by western herbal medicine; Echinacea purpurea, E.angustifolia and E.pallida, as well as the chamomiles (Chamomilla recutita and Chamamaelum nobile), and Calendula to name a few.

Immuno-stimulating polysaccharides are found in numerous medicinal plant such as Calendula
Calendula officinalis, especially the flower buds and flowers, contain immune-stimulating polysaccharides


These are molecules which consist of a sugar joined to a non-carbohydrate compound, often an inorganic molecule. Many chemicals found in plants are bound together with a sugar moiety, forming inactive glycosides. These are able to be broken by enzymatic hydrolysis, as and when the plant requires the chemicals.

Many medications are glycosides, rendering otherwise toxic chemicals safe to use. An example is the saponin glycosides (discussed presently) – the basis of arrow poisons.


Lignan is derived from the phenylpropanoids and partly forms the structural component in woody plants. The phenylpropanoid building blocks are built from a C6H3 unit, similar to the way terpenes are built from isoprene units-C5 H8.


Lignans are completely different to lignins. Lignans are one of the major classes of phyto-oestrogenic substances found in plants. Examples being flax seeds (Linum spp), seasame seeds (Sesamum indicum) brassica vegetables, rye (Secale cereale), apricots (Armeniaca vulgaris), and strawberries (Fragaria spp). Lignans are anti-oxidant also.


This large group of plant constituents  are all based on the basic phenolic molecule.


Phenol is a compound with a hydroxyl group (a molecule of one oxygen atom and and hydrogen atom) bound directly to an aromatic ring).




In general the phenols are known to be bactericidal, anti-septic, anthelmintic, and anaesthetic. Simple phenolic acids include salicylic acid, first extracted from willow bark (Salix spp).

The willow (Salix) gave rise to possibly the most important medicinal plant constituent- salicylic acid, the basis of aspirin
Salix fragilis (cracked willow) The discovery of Salicylic acid in willows, then meadowsweet, was ironically a pivotal moment for allopathic medicine, and consequently herbal medicine.

These are a large group of polyphenols found widely in the plant world. Tannins have been used by man for millennia to tan animal hides. They have also been employed for centuries in the treatment of wounds and burns.

This practice utilises their inherent properties of precipitating proteins into insoluble complexes, and combining with these complexes to eventually render them resistant to enzymatic degradation.

This astringent action is helpful when applied to living tissues. As acids, they will impart a sour taste, with a resultant puckering of the protein lining of the mouth and tongue. When drinking red wine, it is the tannins that produce this reaction in the mouth. In the tea plant (Camelia sinensis) and other plants with which we make teas, such as peppermint, the tannins are what you see forming on top of the drink.

Oaks are a medicinal plant that produce copious amounts of tannin
All Oaks (Quercus sp) are high in tannins, so edible parts such as acorns need leaching in water more than once, to reduce the tannin content, and making them edible.


There are two groups of tannins; hydrolysable and condensed tannins.

Hydrolysable tannins are derivatives of simple phenolic acids. In large quantities they are toxic to the liver, which is why plants that contain them in large amounts are unsuitable for use on wounds. They turn brown on exposure to air and are responsible for the brown colour of many plant tinctures.

Condensed tannins are also known as non-hydrolysable tannins. Plant tissues containing tannins will often have a red colour. When heated in acid they tend to group together and polymerise, forming insoluble substances collectively known as tannin reds. These are often seen to form in tinctures when standing for long periods, especially when stored in the light. (Always keep your herbal medicines in a cool dark place!)

The final breakdown product after heating is a substance called catechol. This shows little toxicity to the liver or other ill effects, so their use is to be favoured.

The rose family of plants contain substantial concentrations of tannins. They are one of the reasons that herbs such as meadowsweet help with acid reflux, and why blackberry leaves can help stop bleeding. Knowing that the rose family plants are rich in tannin, can assist the intuitive herbalist in recognising what they may be useful for.

Raspberry (Rubus idaeus) has astringent, rose flavoured leaves.

Cranberry and Bilberry (Vaccinium species) contain both condensed and hydrolysable tannin. Quercus ilex (the holm/holly/evergreen oak) has acorns with the lowest amount of tannin. As well as the tannin-rich acorns,  other nuts we eat raw, such as hazelnuts, sweet chestnuts, and walnuts, all contain tannin.

It is worth noting that all tannins share these properties:

Solubility in water and alcohol but not in organic solvents such as oils or hexane gas.
The forming of precipitates with proteins, nitrogenous bases, polysaccharides, certain alkaloids and some glycosides.

Tannins are basically astringent, although only at the point of contact with the gut wall. They are also acclaimed haemostatics, used externally to arrest haemorrhaging and soothe exposed inflammations. They are of great benefit in treating the surfaces lining the orifices, so that herbs containing tannins are often used as eyewashes, mouthwashes, snuff and as treatments for rectal problems.

Internally, tannins are known to prevent additional cellular secretions, because the exposed cell walls of mucus membranes pucker or contract following contact. Due to the narrow boundary between the interior and exterior of the gut wall, anti-inflammatory effects are enhanced; therefore tannins can be specifically used for controlling symptoms of gastritis, enteritis and inflammatory bowel conditions.



These substances are widely distributed in nature. Some plants such as the citrus fruits, buckwheat (Fagopyrum esculentum), as well as all white and yellow flowers, have significantly high levels.

Essentially there are four main groups of flavonoids:

Including apigenin from celery, luteolin from horsetail (Equisetum arvense). Also included are the isoflavones (isomers of flavones with steroidal properties) eg: genistein in clovers, gorse (Ulex europaeus) and other legumes.

Among them are quercitol (glycoside= rutin) found in buckwheat (Fagopyrum esculentum), rue (Ruta graveolens) and more than half of all plants ever tested, as well as kaempferol, also in more than 50% of plants tested.


Included here are eriodicytol and methyl-eriodicytol, which together make up ‘citrin’ of citrus fruits. The glycoside is hesperidin. Another well-researched flavonone is liquiritigetol in liquorice (Glycyrrhiza glabra).

4)Xanthones Include gentisin from gentian (Gentianella spp).

Viewed as a group, the flavonoids have numerous important pharmacological properties.
Many are diuretic; others are documented as anti-spasmodic, anti-inflammatory, anti-septic, and even anti-tumour, although the main action of the flavonoid group is on the vascular system.
This all became known as a result of research carried out on the so-called ‘bio-flavonoids’, also known as ‘Vitamin P’; and especially on hesperidin and rutin.

There are four main categories of bioflavonoids:

Quercetin (which acts as a backbone or precursor for other flavonoids grouped together as the citrus bioflavonoids – rutin, quercitrin, hesperidin) Quercetin is anti inflammatory, inhibiting the manufacture and release of histamine.
Citrus bioflavonoids
Green tea polyphenols such as catechin, epicatechin, and epigallocatechin gallate.

Bioflavonoids have been called “nature’s biological response modifiers” because they adapt the body’s reactions to allergens, viruses and carcinogens.

They are also known to exert greater anti-oxidant effects than Vitamins C, E, Selenium and Zinc. Bioflavonoids are known to reduce capillary fragility and permeability, as well as being effective in lowering blood pressure.

Allopathic practitioners treating the capillary symptoms of hypertension, diabetes, arsenic poisoning and allergic conditions, often use rutin. Buckwheat has high levels of flavones so is used by herbalists for much the same problems.

Bioflavonoids and Vitamin C (Ascorbic acid)

During 1936, research by Albert von Szent-Gyorgyiin discovered that scurvy was only helped when ascorbic acid was given with bio-flavonoids.
Ascorbic acid is present in fruits and vegetables only with a bio-flavonoid molecule. It is known to act as a regulating factor in the peripheral circulation as well as exhibiting anti-inflammatory and diuretic properties.


These molecules are named after the Greek words anthos meaning flower, and kyanos meaning blue.

Similar in structure to flavonoids, these pigment molecules found in hawthorn, blackberries, and blueberries (Vaccinium spp), are well known anti-oxidants, especially on the circulatory system and can be coloured anything from blue to red.

They are currently subject to much research. These molecules are the glycosides of anthocyanins.


These are molecules built from a backbone of anthocyanidins. They occur in relative abundance in dark coloured fruits such as bilberries, blackcurrants and blackberries.


Also known as oligomeric proanthocyanidins (OPC’s), or condensed tannins. An oligomer (from the Greek oligos- ‘a few’) is a molecule made from a few monomer units (from the Greek mono – ‘one’ and meros – ‘part’), contrasted to polymers, that in principle can be made from an unlimited number of monomers.

Crataegus shiny fruit
Rich in proanthocyanidins, hawthorn berries are a superfood that N.W European people can properly digest, unlike say, goji berries.

They are famously found in hawthorn, bilberries and blackberries and contribute to its medicinal actions. Effects of OPC’s are to increase intracellular vitamin C levels, decrease capillary fragility, scavenging oxidants, and inhibition of collagen destruction.


These molecules are found throughout the plant kingdom and particularly in the leaves of the pea family (Fabaceae). A fermentation product of coumarin (dicoumarol), occurring naturally in spoilt sweet clover, is a potent anti-coagulant, widely known for being the basis of the rat poison ‘warfarin’. It is the coumarins that can be smelt following the cutting of grass.

Coumarin-rich Sweet woodruff (Galium odoratum). A lover of woodlands


These molecules are similar to coumarins in structure. Known for their strong purgative action, they appear in plants as glycosides. Anthraquinones are found in yellow dock-root (Rumex crispus), rhubarbs, senna (Senna alexandrina), alder buckthorn, and Aloe vera.

Volatile (essential oils)

The countless different mixtures found within plant essential oils provide us with some of nature’s most potent medicines. The name essential oil stems from the fact that when they were first distilled, it was believed that the captured volatile components were the material aspect from a medicinal plant spirit essence.

Generally speaking, essential oils are mixtures of hydrocarbons and other oxygenated compounds derived from them. The most common hydrocarbon present is the terpene, a molecule created by successive accumulation of isoprene molecules (C5 H8). With different variations of this building block, a wide range of substances can be synthesised in plants.

Some of these include: Monoterpenes (C10 H16); Sesquiterpenes (C15 H24); Diterpenes (C20 H32); Sesterterpenes (C25 H40; Triterpenes (C30 H48).


The largest constituent group of volatile oils. Monoterpenes are extremely volatile, evaporating at temperatures above 40˚C. They are the top notes detected when inhaling any volatile oil.

Examples include: borneol, camphene, camphor, carvacrol, carvone, citral, citronellal, cymene, cymol, fenchone, geraniol, limonene, linalool, menthol, menthone, nerol, phellandrene, pinene, thujone and thymol.

Monoterpenes have anti-septic properties. Compared to the antiseptic quality of phenol, (the standard pharmaceutical marker for an anti-septic), thymol is 20 times as potent.

Some monoterpenes have fungicidal and anthelmintic effects e.g. thymol, whilst others have a localised circulatory-stimulating rubefacient property, including menthol, camphor and borneol.

For this they are regularly included in ointments and linaments, whereas internally, they produce an expectorant action – examples are cineol from Eucalyptus (Eucalyptus globulus), pinene from garden angelica (Angelica archangelica), and pinene-borneol and others from garden thyme (Thymus vulgaris).

Numerous monoterpenes act on the nervous system. Carminative herbs are known to act through local nerve endings in the gut, producing an anti-spasmodic action. Furthermore, some monoterpenes, including citral from lemon balm, as well as limonene, myrcene, citronellal and citronellol, will have palpable sedative activity, citronellal being most potent. They can exhibit anti-spasmodic action comparable to the morphine alkaloid papaverine.

Other volatile oil constituents include the molecule anethole, which is found in fennel, and reportedly comprises up to 90% of the volatile oil extracted from aniseed (Pimpinella anisum).

Others, such as cineole, are notably found in Eucalyptus and cajaput oil (Melaleuca leucadendron), apiole is found in celery and parsley, and myristicin from nutmeg (Myristica fragrans). These substances, similar to other volatile components, have carminative, anti-septic, expectorant and circulatory stimulant qualities.

Many members of the Allium family also contain volatile sulphurous substances. These are responsible for the distinctive, pungent aroma common in these plants. These include bulb-garlic (Allium sativum), onions (Allium cepa), and many others.


These are the largest group of terpenes in the plant kingdom, but only a few are volatile – notably the azulenes, bisabolol, and farnesene from chamomile and yarrow. Many are very bitter tasting; notably found in the large daisy family.

Sesquiterpenes have a higher molecular weight and are therefore less volatile and less associated with volatile oils. They give rise to the range of different middle and bass notes detected from a particular essential oil. Some of them are volatile however, including the aforementioned azulenes.

These molecules are special in as much as they do not exist in the plant itself but are a product of steam distillation. They will be found in your cup of herbal tea should you have infused the material in a vessel with a lid!

The much valued azulenes are notable for being potent anti-inflammatories and anti-spasmodics, known for reducing tissue reactions of a histamine-induced nature as well as calming the nervous system. They are also strongly anti-septic, as well as exerting a reduction of the anaphylactic shock effect due to allergic responses. They are therefore well indicated for hay fever, allergic asthma, and allergic eczema.

Esters are important constituents of essential oils. Most esters are known to be anti-spasmodic, anti-inflammatory, and calming, as well as being a tonic to the nervous system.

Esters are reportedly the gentlest and safest components of volatile oils and are harmless on the skin. They include geranyl acetate, found in lavender and Eucalyptus; and linalyl acetate, the main constituent in lavender, bergamot (Citrus x bergamia), and clary sage (Salvia sclarea).

Some therapeutic actions of essential oils from Medicinal Plants

Volatile oils are highly permeable and therefore easily pass through fatty membranes. This helps explain their use as antiseptics, whereby they kill pathogenic single celled micro-organisms.

All volatile oils diffuse rapidly into single cell organisms, where they are thought to disrupt internal cellular mechanics. Through this solubility, volatile components are easily distributed throughout our bodies, exerting their antiseptic qualities.

Volatile oils reportedly also trigger increases in white blood cell production, enhancing the body’s own natural defence systems. The respiratory, urinary, and digestive tracts, as well as the skin, nervous system and all our mucosa, are the primary areas where volatile oils exert their range of effects. Tissues that volatile oils come into contact with are stimulated in important ways, such as vaso-dilation and general increased circulation.

When nerve endings in the digestive system are stimulated they produce increases in gastric juice secretion, salivation and appetite. Peristalsis is improved whilst flatulence and colic are relieved.

Volatile oils are notable for exerting important effects on the C.N.S including tranquilizing (dampening down of messenger molecules), whereas peripherally, anti-spasmodic effects are noticeable. Digestive conditions such as dyspepsia are known to be relieved through the relaxation of internal tissues brought on by volatile oils.

Asthma will be greatly assisted by relaxation of the bronchioles, which can feedback to relieve tensions often found elsewhere in the C.N.S. It is always worth remembering that tensions can be arrested and soothed as much ‘from the neck down’ as by any sedating of the mind. As we are aware, simply smelling a flower and its volatile oils can instantly evoke strong feelings and memories.


These are a complex group of solid and occasionally liquid substances. They are insoluble in water, but soluble in alcohol, ether and chloroform. A number of plants produce them as self-defensive, protective mechanisms, either as a result of injury or pathogenic attack. Other plants produce them as a matter of course during flowering.

Essential resins are a mixture of resin alcohols, acids and phenols, esters and other inert substances. These can be fashioned with essential oils and gums to create ‘oleo-resins’ and ‘gum-resins’, or even compounded to create ‘oleo-gum-resins’.

Pines (Pinus spp) produce well known sticky resins. Cannabis (Cannabis sativa) and hops both produce an ‘oleo-resin’, whilst myrrh (Commiphora molmol) and frankincense (Boswellia spp) contain oleo-gum-resins. Some of the medicinal effects of the resins include the stimulation of phagocytosis (white blood cell’s destruction of harmful bacteria), and anti-septic qualities.


The term is derived from the Latin word for soap – sapo, hence exhibiting ‘frothyness’ in solution. Saponins are the major constituent within soapwort (Saponaria offiicinalis), a plant whose roots have long been used as a soap. They are also found in many different plants.

Originally known medically for their haemolytic (destruction of red blood cells) properties, saponin-containing plants long been employed as arrow poisons and fish poisons. Incidentally, saponins are toxic to all animals if intravenously injected, which is one reason why whole plant extracts are not administered in this way. Saponin containing plants are covered over on my poisonous plants page.

However, it is the property of the whole saponin molecule that is toxic. When they are ingested, the whole glycoside molecule is quickly broken down in the stomach, leaving the pharmacologically active, sugarless ‘aglycone’. This sugarless saponin is not haemolytic to humans. However, fish and other cold-blooded creatures are always poisoned by saponins, in any form.

The steroidal form of saponin is found in the majority of plants. Steroidal saponins have structural similarity with steroid hormones, cardiac glycosides, and vitamin D. They are the framework for modern production of synthetic hormones. The contraceptive hormone dioscin was first synthesised from an extract of the yam.

Many saponins act on the respiratory system, where there presumed action is again thought to be by reflex action, this time as a result of their reported emetic effect if taken in higher doses. At doses well below this they are acknowledge to stimulate expectorant activity, notably in mullein, elecampagne and liquorice.

Some can settle the stomach, aiding the absorption of minerals. Oats (Avena sativa) are a suitable saponin-containing remedy for this. Other saponins are anti-inflammatory, such as those found in sweet-corn silks (Zea mays) and silver birch.


These pigment molecules are derived from the triterpene skeleton. Closely related to vitamin A (converting to it in the body), carotenoids are found in many orange and red pigments in plants, for example, lycopene from tomatoes (Lycoperiscon esculentum) and beta-carotene from garden carrots (Daucus carota ssp sativus).

Cardiac glycosides

Alongside the opiates, these are possibly the most studied of all the plant constituents. Cardiac glycosides reportedly have very similar properties to steroidal saponins, and are found together in many plants. Cardiac glycosides have a well established use in preventing unpleasant symptoms of heart failure such as the aggregation of fluids, whilst also combating shortness of breath when lying down.

They were famously extracted from a folk-remedy for ‘dropsy’ during the latter part of the 18th century by a Shropshire doctor, intent on isolating the miraculous active principle. The remedy included foxglove, which the doctor knew from experience to be the active principle. The molecule digitoxin was finally isolated in 1875, with digoxin later isolated and used since 1957.

The effects of cardiac glycosides such as digoxin are known to vary with the condition of the heart muscle cells, and the dosage. The use of these potent drugs by clinically untrained people cannot be recommended.

Cyanogenic glycosides

These molecules take their name from the breakdown products after hydrolysis – prussic acid (hydrogen cyanide). Therefore in any quantity these compounds are very toxic. They are one of the primary constituents responsible for the aroma and flavour of bitter almonds and are common in many stone fruits of the rose family such as peaches, apricots, and hawthorns as well as being found in the elder and clover. This all leads to the question…what is edible anyway?

By using plant medicines with small amounts of cyanogenic glycosides, noticeable anti-spasmodic and sedative effects are produced. They also have an effect on the parasympathetic nervous system, slowing the heart-rate and improving digestion. The lungs are known to excrete these molecules quickly.

Mustard oil glycosides

Otherwise known as glucosilonates, these molecules are found in the brassica family. More than 60 compounds have been isolated and they are responsible for the pungent aroma from members of this large family. The smell of mustard oil glycosides are one of the patterns that we can use to identify brassicas. You can read more in this  discussion of the easy-to-learn patterns method of plant identification

Plants containing these glycosides are used mainly to increase blood flow to membranes they contact. Hence their use as rubefacients to increase local blood flow. A classic example of their traditional use is the mustard footbath.

As a group, these acrid molecules were mainly known for stimulating and toning the circulation, slowing the heart rate, and improving digestion. Glucosilinates are said to increase anti-oxidant defence mechanisms as well as improving the body’s inherent ability to detoxify and eliminate harmful chemicals. They are present in watercress the subject of much anti-cancer research, discussed presently.


These are central components within any herbal approach to treatment. Most plant remedies have at least a small amount of bitterness. The diverse range of bitter principles in plants amounts to the largest and most diverse group of plant constituents. Bitters will only work through the bitter tasting receptors in the mouth and have no effect if taken as a capsule or masked by syrups. They produce a number of reactions including:

  • Increasing gastric acid secretions

  • Stimulating pepsin secretions

  • Stimulating pancreatic digestive secretions

  • Intestinal juice production

  • Hepatic bile flow

  • Insulin derived glucagon secretions

  • Toning the muscle of the lower oesophageal sphincter

  • Toning the muscle of stomach wall and small intestine

  • Cell division and growth of gastric and duodenal mucosa

  • Cell division and growth of the pancreas



These are probably the most studied and some of the most potent and toxic plant products. Most plants have at least some alkaloids in them. Chemists have divided the alkaloids into various groups in order to reflect their different origins (biosynthetic pathways) within plants.

Pyrrollidine alkaloids

These come from the amino acid ornithine. They act on the parasympathetic nervous system, blocking nerve activity. Included here are cocaine, hyoscyamine, scopolamine, hyoscine and atropine. Many of the Solanaceae plants including henbane, datura, belladonna, and bittersweet, contain these types of alkaloids.

Pyrrolizidine alkaloids

This group of alkaloids have a reputation for notable toxicity, linked with liver damage. This is another group emanating from the amino acid ornithine, found in ragworts (Senecio spp), coltsfoot, and the borage family – famously comfrey. The potential risks from eating comfrey is addressed in the material medica

Indole alkaloids are built from the amino acid tryptamine. Included here are the mood molecules (see nervous system chapter) such as serotonin, adrenaline, and noradrenaline, as well as the tranquillizing alkaloids found within the numerous passionflowers. Also of note are the products of ergotamine, such as lysergic acid diethylamide (L.S.D), and the well documented central nervous stimulants strychnine (famously found in Strychnos nux vomica), johimbine (from Corynanthe yohimbe syn Pausinystalia yohimbe), and psilocybin, the latter being found in ‘magic’ mushrooms.

Quinoline alkaloids 

These include the anti-malarial drug quinine which gives its name to this group of molecules. This substance was originally derived from Cinchona ledgeriana. Also included here are the isoquinolines. They are all constructed from the amino acid phenylalanine. Notable extracts include mescaline from the low-growing peyote cactus (Lophophora williamsii), the opiate alkaloid papaverine and the compounds berberine and hydrastine from Berberis species.

Purine alkaloids

These are derived from the nucleotides adenine and guanine and act on the nervous system, prolonging the life of many secreted hormones including adrenaline. Included in this group are the xanthine alkaloids caffeine, theobromine, theophyllene, and aminophyllene from coffee shrubs (Coffea arabica), cocoa (Theobroma cacao), and the tea plant (Camelia sinensis) respectively.

Cancer preventative compounds in fruits and vegetables

Vegetables, fruits and whole grains contain an impressive array of phyto-chemicals that are increasingly recognised as being of help to regulate and negate cancer development.

Various studies and tests suggest that diets rich in fruits and vegetables are associated with reduced risks for a number of common cancers. Hundreds of potentially valuable substances have been identified by food chemists and natural product scientists. Many are being evaluated for the prevention of cancers, although the varied mechanisms of action of the majority of plant constituents in cancer prevention are still unclear.

The following groups of molecules are all currently subject to research:


These are a diverse, structurally related group of compounds synthesised by plants and bacteria. The fact that these molecules are anti-oxidants, able to quench single oxygen atoms, has led to many theories and hypotheses regarding their roles in preventing disease processes, especially ones related to chronic oxidative damage such as cancer and cardio-vascular disease.

Recent research has suggested that carotenoids may also modulate processes such as mutagenesis (where the information of an organism is changed – usually within nature in a stable manner), cell differentiation and cell proliferation, independently of their role as anti-oxidants or pre-cursors of vitamin A. Some studies have revealed that increased consumption of beta-carotene rich foods, as well as higher blood levels of beta-carotene are associated with a reduced risk of lung cancer. Both lutein and lycopene, among the most abundant of carotenoids, are known to exhibit exceptionally strong anti-oxidant activity.

Dietary sources include carrots and tomatoes and all red/orange pigmented food as well as green leafy vegetables. A recent fad for ‘goji berries’, a close relative of the tomato, can be partially explained by the presence of carotenoids amongst other anti-oxidants. It is cheaper and surely wiser to source our common plants such as rowans, hawthorns, and rosehips for similar effects.


This molecule, and its derivative chlorophyllin, have both shown to exert profound anti-mutagenic behaviour against a wide range of potential human carcinogens. Some researchers have postulated that a reduced carcinogen uptake may be because of the complexes that chlorophyllin forms with carcinogens in the diet or digestive tract.

One recent study indicated that the amount of chlorophyllin required to protect against aflatoxin-induced-liver-carcinogenesis was less than 1500 parts per million (p.p.m). Aflatoxins are toxins produced by fungi especially members of Aspergillus fungi. They contaminate cereals before harvest and during storage. Chlorophyll concentrations within spinach are in the region of 150-600,000 p.p.m, dependent on soils. All green leaves contain chlorophyll in varying concentrations. Algae are rightly recognised as a superfood due to their abundance of chlorophyll as well as the high amounts of amino-acids and trace elements.


These compounds are ubiquitously found in fruits and vegetables and known to have an array of biological activities including oestrogenic effects. Pharmacological effects are reportedly due to their inhibition of certain enzymes as well as their anti-oxidant activity.

Certain flavonoids and the isoflavones (present in significant amounts in the pea family), are thought to act as competitors for hormone binding sites, preventing oestrogen induced stimulation of breast tumour. Ordinarily flavonoids are widely distributed in a healthy diet and are abundant in grapes (Vites spp), cereal grains (Poaceae family), tea, citrus fruits, buckwheat, umbelliferous vegetables, brassicas, and tomatoes.


The compound indole-3-carbinol is a compound derived in the acid conditions of the stomach from glucobrassicin, found in cruciferous vegetables. During digestion, many derivatives of indole-3-carbinol are produced, and these molecules act as a trigger to induce specific enzymes.

The production of these enzymes, including cytochrome P450 and glutathione S-transferase, is known to result in increased metabolic activity towards chemical carcinogens. They contribute towards the known anti-carcinogenic properties of inole-3-carbinol, as well as the reduced risk of cancer associated with diets rich in brassicas.

Broccoli (Brassica oleraceae var botrytis ) is high in indole-3-carbinol and glucosilinates and contains the carotenoid lutein. Indole-3-carbinol has been reported to help arrest the growth of prostate cancer (although mechanisms remain unclear), whilst it also decreases growth in human papilloma-virus.


These organic molecules are widely distributed in plants. They have distinctive, characteristic flavours and odours in addition to their variety of pharmacological and toxic activities. Many brassica’s including watercress leaves contain the isothiocynate molecule gluconasturtiin.

This compound is transformed by the act of chewing into phenethyl isothiocynates (PEITC), which is responsible for the sharp taste of the plant.

Watercress consumption relating to cancerous growth was increasingly studied after it was discovered that dietary doses of watercress and the resultant PEITC increases urinary excretion of NKK (4-methylnitrosamino-1-3-pyridyl-1-butanone) metabolites in smokers.

NKK is a proven potent pulmonary carcinogen in rodents and is believed to be one of the causes of human lung cancer. Inhibition of the various metabolic activation pathways of NKK by PEITC results in increased excretion of harmful metabolites in urine.


Polyphenolic compounds

These molecules are believed to act as antioxidants or as some other agent contributing towards anti-carcinognic or cardio-protective actions. Ellagic acid, a polyphenolic molecule generated from ellagitannins has been viewed as one of the most promising chemo-preventative agents for reducing risk of human cancers.

The ellagitannins are a chemically complex group of substances. Ellagic acid is found in substantial amounts in grapes, strawberries, raspberries, cabbage, whilst another polyphenol compound, curcumin, is found in ginger and turmeric. These compounds work by scavenging oxygen radicals involved in oxidative destruction of membrane lipids, through the inhibition or induction of certain enzymes.

Sulphur based compounds

Sulphides have been shown to inhibit a variety of tumours induced by chemical carcinogenesis. Topical applications of oil-soluble diallyl sulphide and diallyl disulphide (both are found in garlic, onions and brassica’s) significantly inhibited skin papilloma formation as well as increasing the rate of survival in mice.

Sulphoraphanes are also found in broccoli. They are noted for increasing the rate by which the specific form of oestrogen linked to breast cancer – known as 2-hydroxyestrone, can be broken down through the liver by up to 50%.

Tests on animals found sulphoraphane inhibited breast cancer growth. When topically applied, sulphoraphane may protect against U.V radiation damage, and thus potentially against cancer. These molecules are being investigated in numerous clinical trials.

Recent research has revealed that broccoli seed sprouts contain 30 to 50 times as much sulphoraphane as mature plants, helping our body produce detoxifying enzymes as well as exerting anti-oxidant effects. 30g of sprouts is considered to be worth 1kg of mature heads.


These molecules are known to exhibit a diverse range of metabolic, cellular and molecular activities. Compounds under investigation include geraniol and farnesol, which have shown in tests on animals to inhibit pancreatic cancers.

The terpene perillyl alcohol (POH) is the hydroxylated analogue of delta-limonene. Essentially this means that these two molecules are structurally identical, except that POH has an extra oxygen atom.

Both of these compounds have been shown to help prevent carcinogenisis at the initiation and progression stages of liver cancer, lung cancer, U.V-induced skin cancer, and breast cancer development.

The effects are believed partly due to their inhibition of the production of certain proteins which then trigger altered gene expression. Perillyl alcohol is absorbed from the gut and metabolised to what are considered the active metabolites, perillic acid and dihydroperillic acid.

Studies have revealed that POH is more than 5 times more potent than delta-limonene at inducing tumour regression. Dietary terpenes are found widely in citrus fruits such as lemon, grapefruit, lime, and orange, as well as in lavender, mints, celery seeds, and cherries.


Whole grains

The substances found in whole grains are similar to those found in fruits and vegetables. They include: sterols, phytases, phyto-oestrogens, lignans, ellagic acid, and saponins. Because the phyto-chemicals are concentrated in the germ and the bran, to ensure and to maximise health benefits, it is necessary to consume the whole grain. Refinement of wheat or rice, for example, massively reduces the phyto-chemical content!


2 thoughts on “Medicinal Plant Constituents and Actions”

  1. Hey,

    I just wanted to say that this is such a great article on plant constituents, so interesting and thorough. I am using it as a reference in my herbal dissertation.
    Thanks a million,


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