The medicinal effects of certain plants are well known. Aloe vera was known to Cleopetra as a healing skin remedy. The active constituents are responsible for the medicinal actions of plants. Knowing a little about the chemical contained in the plants helps us to understand how they work within the body.

PHENOLS
Phenols are a very varied group of plant constituents ranging from salicylic acid, a molecule similar to aspirin (acetylsalicylic acid), to complex sugar-containing phenolic glycosides. Phenols are often anti-inflammatory and antiseptic and are thought to be produced by plants to protect against infection and feeding by insects. Phenolic acids are strongly antioxidant and anti-inflammatory and also have antiviral properties. Such as – Hemp (Cannabis sativa) Pg 192, cherry (Prunus sp), dark plum, black mustard seed (Brassica sp), clove (Syzygium aromaticum), cumin (Carum carvi) Pg. 202, tea (Cameillia sp), coffee (Coffea sp), Aloe vera, Salix alba.

FLAVONOIDS
Flavonoids are polyphenolic compounds that act as pigments, imparting colour, often yellow or white, to flowers and fruits. They have a wide range of actions and many medicinal uses. They are antioxidant and especially useful in maintaining a healthy circulation. Some flavonoids have anti inflammatory, antiviral and liver protective activity. Flavonoids such as hesparidin and rutin, found in many plants, notably buckwheat (Fagopyrum esculentum) and lemon, strengthen capillaries and prevent leakage into surrounding tissues. Sometimes isoflavone are estrogenic and valuable in treating menopausal symptoms. Some flavone containing plants are Cassia senna, celery (Apium graveolens) Pg 76, Polygonum sp, Euisetum arvense.

VOLATILE OIL
Volatile oils – which extracted from plants to produce essential oils – are some of the most important medicinally active plant constituents and are also used widely in perfumery. They are complex mixture often 100 or more compounds, mostly made up of monoterpenes – molecules containing 10 carbon atoms. Essential oils have many uses. Some of them is anti-inflammatory and anti analgesic. Tea oil is strongly antiseptic.  Some essential oils used as insect repellent. On distillation some essential oil contain compound not found in the volatile oil. Carum carvi seeds contain volatile oil which are antiseptic, antispasmodic, carminative digestive, expectorant, galactogouge and stimulant.  Volatile oils are derived from various parts of plants, such as – Bark – cinnamon. Wood - camphor, sandalwood. Leaves – bay-leaves, basil, cinnamon, lemon grass, eucalyptus, piper mint, thyme. Flowers – chamomile, clove, hyssop, lavender, rose, marjoram. Rhizome – zinger.   
Resins – sticky oily substance that seep from plants, are often linked with essential oils (oleo-resins) and gums, they are non-volatile.

TANNINS
Tannins are produces to a greater or lesser degree by all plants. The harsh astringent taste of tannin- laden bark and leaves make them unpalatable to insect and grazing animals. Tannins are polyphenolic compounds that contract and astringe tissues of the body by binding with and precipitating proteins – hence their used to “tan” leather. They also help to stop bleeding and to check infection. Tannin containing herbs are used to tighten up over relaxed tissues – as in varicose veins to dry up excessive watery secretions – as in diarhhoea and to protect damage tissues – such as skin problems resulting from eczema and burn. Black catechu (Acacia catechu) Pg. 7 is high in tannins. Wood, leaves and seed husks of Sweet chestnut (Castanea sativa) Pg. 204 contain good amount of tannin. Bark and leaves of Indian Chestnut (Castonopsis indica) Pg. 206 contain tannin 6 – 12% and 10% respectively. Common smoke tree (Cotinus coggygria) Pg. 261 bark contain 8 -12% tannins.
 
PROANTHOCYANINS
Proanthocyannins is closely related to tannins and flavonoids. Polyphenolic compounds are pigments, which give flowers and fruits a blue, purple or red colour. They are powerfully antioxidant and free radical scavengers. They protect the circulation from damage, especially the circulation in the heart, hand, feet and eyes. Blackberry (Rubus fruticosus), red grapes (Vitis vinifera) all contain appreciable quantities of these proanthocyannins.
 
COUMARINS
Coumarins of different kinds are found in many plant species and have widely divergent actions. The coumarins in some species helps to keep the blood thin, while furanocoumarin such as bergapten, found in celery (Apium graveolens), stimulate skin tanning. Dentatin and nordentatin are two coumarins isolated from Clausena dentate, apricot (Prunus) cinnamon (Cinnamomum) Pg. 288, strawberries (Fragaria sp), cherry (Prunus sp) and different kinds of coumarins in good amount are isolated from roots of Heracleum sp.
 
ANTHRAQUINONES
Anthraquinones are the main active constituents in herb such as senna (Cassia senna) and Chinese rhubarb (Rheum palmatum), both of which are taken to relieve constipation. Anthraquinone have an irritant laxative effect on the large intestine, causing contractions of the intestinal walls and stimulating a bowel movement approximately 10 hours after being taken. They also make the stool more liquid, easing bowel movements.
 
SAPONINS
Saponins are the main active constituents of many medicinal plants; they gained this name because, like soap, they make lather when placed in water. Saponins occur in two different forms – steroidal and triterpenoid.  The chemical structure of steroidal saponins is similar to that of many of the body’s hormones, for example estrogen and cortisol, and many plants containing them have a marked hormonal activity. Wild yam (Dioscorea villosa) from which the contraceptive pill was first developed contains steroidal saponins. Terpenoid saponins occur more commonly  - for example liquorices (Glycyrrhiza glabra) has less hormonal activity. It is often expectorant and aid absorption of nutrients. Other plants containing saponins include horse chestnut tree (Aesculus hippocastanum) and asparagus fern (Asparagus oficinalis).

CARDIAC GLYCOSIDES

Glycosides found in various medicinal plants – Adonis aestivalis, Adonis vernalis, foxgloves (Digitalis lanata, Digitalis purpurea), common oleander (Nerium sp), yellow oleander (Thevetia sp), wallflower (Cheiranthus sp), squill (Urginea sp); notably in Digitalis sp. Cardiac glycosides such as digitoxin and convallotoxin have a strong, direct action on the heart, supporting its strength and rate of contraction when it is failing. Cardiac glycosides are also significantly diuretic. They help to stimulate urine production, thus increasing the removal of fluid from the tissues and circulatory system.

CYANOGENIC GLYCOSIDES

Cyanogenic glycoside based on cyanide, a very patent poison; in small doses they have a useful sedative and relaxant effect on the heart and muscles. The barks of wild cherry contain cyanogenic glycosides, which contribute to the plant’s ability to suppress and soothe irritant dry coughs. Many fruit kernels contain high level of cyanogenic glycosides, for example those of apple, apricot (Prunus armeniaca), cherry (Prunus sp), Hawthorn (Crataegus oxycantha).

POLYSACCHARIDES

Polysaccharides are multiple units of sugar molecules linked together, found in all plants. From herbal point of view sticky mucilage and gums are the most important polysaccharides, which are commonly found in root, bark, leaves and seeds. Both mucilage and gum soak up large quantities of water, producing a large jelly like substance that can be used to soothe and protect irritated tissues. Mucilaginous herbs are best prepared by soaking (macerating) in plenty of cold water. Some polysaccharides stimulate the immune system, for example acemannan, which is found in the leaves of aloe vera (Aloe vera) . Rice (Oryza sativa), maze (Zea maze), potato are rich sources of starch.

GLUCOSILINATES
Glucosilinates found exclusively in species of mustard and cabbage family, these constituents have an irritant effect on the skin, causing inflammation and blistering. Applied as poultice to painful joints, they increase blood flow of the affected area, helping to remove the built up waste product (contributory factors in many joints problems). On eating, glucosilinates are broken down and produce a strong pungent taste. Cabbages, Radish (Raphanus sativus), garlic (Allium sativum) are typical glucosilinate containing plants.

BITTERS
Bitters are varied group of constituents linked only by their pronounced bitter taste. The bitterness itself stimulates secretions by salivary glands and digestive organs. Such secretion dramatically improve the appetite and strengthen the over all function of the digestive system. Many herbs have bitter constituents, notably wormwood (Artemisia absinthium), chireta (swertia chirata), ipecac (Cephalis ipecacuanha), hops (Humulus lupulus), Indian star thistle (Centaurea iberica) – root.

 ALKALOIDS
A mixed group, alkaloids mostly contain a nitrogen-bearing molecule (-NH2) that makes them particularly pharmacologically active. Some are well known drugs and have a recognized medicinal use. Vincristin form Vinca rosea, is used to treat some types of cancer. Other alkaloid such as atropin from Atropa belladonna Pg. 135, have a direct effect on the body, reducing spasms, relieving pain and drying up bodily secretions. Indian root of Ipecac (Cephalis ipecacuanha) contain 1.98% of total alkaloids, nicotine from tobacco (Nicotiana tabacum), caffeine from coffee (Coffea arabica), cocaine from coca (Erythroxylum coca) are stimulant, opium from poppy (Papaver somniferum) is a pain relieving, and taxol from Taxus buccata is narcotive.

VITAMINS
Many medicinal plants contains different kinds of vitamins. Some plants are well known for their vitamin content, for example lemon, amla (Phyllanthus emblica), chili (Capsicum sp), are a rich source of vitamin C. Vegetable oil, green leafy vegetables, nuts are rich source of vitamin E, and carrot (Daucus carota) is rich in beta-carotene (pro-vitamin A).  Many plants are less well recognized & some contain vitamin B1, B2, E, etc.

MINERALS
Like vegetable, many medicinal plants provide high level of minerals. Plants, specially organically grown, draw mineral from the soil and convert them into a form that is most easily absorbed and used by the body. Whether plants are eaten as a vegetable, like cabbage (Brassica oleracea) or taken as medicine. In many cases the mineral content is a key factor in the plant’s therapeutic activity within the body. Dandelion leaf (Taraxacum officinale) is a potent diuretic, balanced by its high potassium content, while the high silica content of horsetail (Equisetum arvense) supports the repair of connective tissues, making it useful in arthritis.