Clinical herbal therapy employs several different methods of presenting the herbal material to the body, and dosages are precisely calibrated according to individual need , all of these variables having significant impact on the efficacy of the remedial action.
Three main methods of extraction are in common usage: Water extraction, Solvent extraction and Fat extraction. Each method offers different extractive properties, applications and usefulness under various circumstances.
For the amateur herbalist, and also in certain clinical situations, water extractions can be very useful. The methods employed are infusions and decoctions. These are very similar techniques.
An infusion is used for leaves, flowers and other soft parts of the plant. The herbal material is placed in a suitable vessel and boiling water being poured over. The infusion is steeped for 5 to 15 minutes. A decoction is used for barks, roots, berries and any hard parts of the plant. The herbal material is placed in a pan, covered with cold water and brought to the boil. It is covered and allowed to simmer for 5 to 15 minutes.
An infusion or decoction may also be made cold. The plant material and water is allowed to stand at room temperature overnight before being strained off. This is useful where there are many volatile oils that may be lost if heat is used (eg. Sweet flag (Acorus calamus), or where there is a lot of mucilage that would cause the end product to be very thick and glutinous (eg. Marshmallow (Althea officinalis).
In both of these cases, the water acts as a solvent to extract only those constituents which are soluble in water. It may be usefully employed to extract tannins, bitters and glycosides, but is not appropriate for extraction of resins, volatile and non-volatile oils or alkaloids. In the case of volatile oils, although they will not actually dissolve in water, they will evaporate in the heat and they will float on the top of the water and arise in the steam.
Advantages of water extraction are that it is quick, cheap and easy, requires no special expertise nor any special equipment or ingredients. Disadvantages of water extraction are that it does not extract all therapeutically useful constituents, that the resulting herbal remedy does not have a long shelf life (an infusion or decoction will last only about 24 hours in the fridge before bacterial contamination becomes a concern), and that it is hard to standardise the end product. It is also worth noting that infusions and decoctions often taste very unpleasant and this may reduce the compliance rate and hence the efficacy of the remedy.
This is the method commonly employed by herbal practitioners. The herbal material (marc) is soaked for 2 weeks in an organic solvent diluted to a specific percentage with water (menstruum), after which the liquid is squeezed off and that becomes the medicine while the herbal remainder is discarded.
Some solvents that may be used include:
1) Vinegar (acetracta)
This is about 4% acetic acid which is excreted via the lungs, kidney and skin where it acts as a mild expectorant, diuretic and diaphoretic. An acetracta may be useful when administering herbs to a small child or a person with compromised liver function because vinegar is very gentle on the body. Vinegar is a reasonably good solvent but the shelf life of an acetracta is only about 3 months. Because of the unpleasant taste the medicine is frequently mixed with honey, in which case it is called an oxymel.
2) Glycerine (glycetratca)
This is a colourless, odourless, viscous fluid with solvent capacities somewhere between alcohol and water. A glycetracta is commonly used to preserve fresh expressed plant juices (in the ratio 1:1) and to make syrups. The taste is sweet and the shelf life is 6 to 12 months.
3) Alcohol (tincture)
For commercial preparations, an alcohol solvent is the most useful. Usually the alcohol used is ethyl alcohol (96.4% strength). Commercial ethyl alcohol is usually made from corn to which many people are sensitive. For further information on how ingestion of corn-based alcohol can intereact with a corn allergy to play havoc with your health see the excellent book Allergies- Your Hidden Enemy by Theron Randolf MD and Ralph moss PhD. (Thosrsons 1986). Alcohol made from sugar beets may reduce the incidence of allergies to tinctures. Pesticide-free grape alcohol has recently become available as well. A tincture will extract all fat soluble constituents and, because the tincture is also made with water, you can be reasonably sure of accessing all the useful parts of the plant. Note that the tincture must be at least 25% alcohol to ensure sterility and that different herbs require more or less alcohol to access the different constituents. Foe example, Cayenne (Capsicum minimum) and Ginger (Zingiber officinalis) both require 90% alcohol to provide maximum extraction of medicinal resins, but Red raspberry (Rubus idaeus) and Plantain (Plantago lanceolata) only require 25% alcohol to extract the water soluble tannins. A tincture has the advantages that it extracts well, is convenient to dispense, easy for the patient and has a shelf life of up to 3 years.
Using fat as a solvent will extract those constituents that are fat or alcohol soluble: gums, resins, fixed and volatile oils, waxes and alkaloids. There are three methods used:
- Enfleurage. Fresh plant material (usually flowers) is placed over a layer of fat with a low boiling point (eg. cocoa butter) and allowed to stand for 3 days at room temperature. A mild organic solvent (alcohol) can then be used to extract the plant constituents from the fat.
- Digestion. This is done in a similar way to enfleurage but the fat is heated to about 350 C and maintained at that level for several hours to a few days. The warm oil ‘digests’ the plant material and draws out the fat-soluble constituents. The oil is then squeezed out of the plant material.
- Infusion. Plant material is placed in a jar with vegetable oil (usually almond or olive) and allowed to stand at room temperature for up to 2 weeks. The oil is then squeezed out of the plant material.
For most purposes the infusion method is preferrred. It involves no heat so preserving all the therapeutic propertes of the plant. It is also easy to incorporate the resulting medicated oil into salves or liniments. The digestion method is advantegeous when speed is important, because it can be made in 24 hours as compared to 2 weeks for an infused oil. The enfleurage method is only used nowadays for the extraction of few extremely heat-sensitive volatile oils such as Jasmine, Neroli and Rose.
Having made a herbal extract with water, a solvent or fat, you then are able to incorporate the remedy into various mediums and apply them in various ways. Eg. water extractions may be employed in number of ways: the tea may be drunk, or it may be used as a mouth wash, gargle, compress, skin wash, eye wash, douche, enema, hair rinse and so on. Tinctures may be diluted as internal medicines or may be used in all the same ways as a water extraction. Acetracta and glycetracta are almost exclusively used internally. Fat extractions are almost always applied externally in the form of skin oils or incorporated into ointments, lotions and creams. A cocoa butter extraction may also beused as the bas efor suppositiories. Infusions, decoctions and solvent extractions may also be spray dried and incorporated into tablets. A final common method of preparing herbs for internal use is to make capsules. The herb is either air dried or freeze dried, ground and used to fill gelatin capsules. This has the advantages of being cheap and convenient but the shelf life tends to fairly short with oxidation of the herb being a very real concern.
These methods of herbal extraction are the traditional and time-honoured ways. They are still entirely viable in the modern world because they are simple, cheap and effective.
|Oral||Mucus lining of the
tincture, acetracta, glycetracta,
capsule, tablet, or taken in the form of
|Convenient & painless.
Remedy passes first to the liver where
potentially toxic agents may be
|Absorption is slow,
irregular and unpredictable and thus is
not suitable when a fast or precise
response is important. Because the
remedy passes first to the liver there
is a possibility that useful
constituents are broken down before
reaching other parts of the body.
|Sub-lingual||Mucus lining of the
|Lozenges, tablets, spray||Uptake into the
bloodstream is very rapid (usually
within 2 minutes). Enters the systemic
circulation directly without first
passing through the liver.
|Only a few remedies can
be administered in this way. May be
dangerous to avoid the first pass
through the liver which acts as a filter
or screen for many toxic substances.
|Rectal.||Mucus lining of the
|Suppositories or enemas||Can be used in the
vomiting, comatose or uncooperative
patient Useful for remedies which would
cause nausea or vomiting if given orally
|Bypasses the liver and
enters the systemic circulation
directly. Rectal route may be
unacceptable to some sensitive patients
|Mucus lining of the
|Pessaries, creams or
|Permits local treatment
with very little being absorbed into the
|May be messy or
unacceptable to some patients. Not
suitable during pregnancy.
|Mucus lining of the nose
and upper respiratory tract, the
|Sprays, aerosols and
|Uptake is almost
instantaneous, and a very local effect
may be obtained
|May be some absorption
into the systemic circulation. The
technique may be difficult for some
liniments, powders, poultices and
|A very local effect can
be obtained. May be possible to get
better access to a poorly vascularized
area from the outside (eg. a capsicum
plaster over an arthritic joint).
|Some absorption may occur
into the systemic circulation and this
may be variable and unpredictable.
Dosages and Frequencies in Herbal Medicine
The first thing to consider is that dosage and frequency must depend upon several factors: the strength or concentration of the remedy, the severity of the symptoms and the underlying physiological strength of the system or person. Thus, for example, a large, muscular man in generally good health but suffering from an acute head cold will tolerate and, indeed, need, a much higher dose of herbal medicine than would a frail old lady with chronic arthritis, or a 5 year old child with emotionally-based asthma.
In general, acute conditions will require higher doses and/or stronger medicines than will chronic conditions. Likewise, a small body requires less than a large body. Those people with compromised liver function will metabolize their remedies differently and may need lower doses to prevent a cumulative action. The same is true for people with impaired kidney function who may not be able to excrete remedies as fast as could otherwise be expected.
Children and the elderly are particularly at risk of liver or kidney insufficiency, but previous medical history, current complaint, other drugs or remedies being used and alcohol & drug abuse should all be taken into account when determining a dose.
Another factor to consider when estimating the dose is whether there is any concomitant constipation or diarrhoea. If there is hypermotility of the gastro-intestinal tract then a remedy will pass rapidly thorough the system and not as much will be absorbed as in the case of hypomotility.
Biochemical assays, clinical research and empirical evidence have been amalgamated to create a solid body of knowledge about the safety and efficacy of very many herbs. In the British Herbal Pharmacopoeia of 1983 dosages are given for over 200 herbs and they range from small doses (eg. 0.5 ml. three times daily for a 1:5 tincture of poisonous herbs such as Deadly nightshade (Atropa belladonna) to large doses (eg. up to 10 mls. three times daily for a 1:5 tincture of Taraxacum off. radix). For most herbs in the B.H.P. the typical dose is between 2 and 6 mls. three times daily for a 1:5 tincture.