Herbs are sold in many forms, as fresh plant material in the produce department of a grocery store, and as dried plant material in bulk, tea bags, capsules, or tablets. Fresh or dried plant material can be prepared as extracts, either sold in liquid form, or dried and formulated into tablets or capsules, both hard and soft.

The diversity in plant preparations is illustrated by those available for commercially supplied Asian ginseng roots, which are graded according to their source, age, part of the root, and method of preparation (Bahrke and Morgan, 1994).

The root can be used fresh, or prepared as “white” ginseng (peeled and dried) or “red” ginseng (steamed and dried). The fresh root is often thinly sliced and taken with or without honey, or it can be boiled in soup. White or red ginseng can be powdered, extracted, or made into a tea (Yun and Choi, 1998).

The different ginseng root preparations differ in their chemical composition. As an example, we know that the heating process in the production of red ginseng converts the malonylginsenosides to their ginsenoside counterparts and also results in other chemical transformations (Chuang et al., 1995).

The preparations described are, by definition, of different strengths and composition. Thus the type of preparation will have an influence on the recommended dose. Teas prepared with hot water are usually quite dilute in contrast with extracts that are more concentrated.

So it follows that the type of preparation must be taken into account in determining the dose. For example, peppermint tea may be drunk by the cupful, while peppermint oil is administered in doses of five hundredths of a milliliter (Wren, 1988).

The type of preparation, and formulation of the preparation, will have an influence on the ability of the chemical components of the herb to be assimilated into the body. This is especially a concern with tablets and capsules whose contents must first dissolve before being absorbed.

Coatings on the surface of tablet or capsules may be designed to either accelerate or delay dissolution (release of chemical constituents) in the gastrointestinal tract. As an example, garlic products often have enteric coatings to delay dissolution until the garlic preparation reaches the intestine.

The reason for this is that garlic powder contains the enzyme allinase, which is necessary to produce the active constituent allicin, and that enzyme is destroyed by the acidic pH of the stomach. Studies on the effectiveness of Kwai garlic to reduce elevated serum cholesterol levels have been inconsistent.

A review found a highly significant difference in effectiveness between studies conducted before 1993 and those conducted in 1993 and later. The authors found that the amount of allicin released under simulated gastrointestinal conditions correlated well with the success or failure of the tablets to lower serum cholesterol values.

The sharp decline in the effectiveness of the tablets is paralleled by sharp declines in both the acid resistance and the allicin release from the tablets, apparently caused by a change in the coating of the tablet (Lawson, Wang, and Papadimitriou, 2001).

Preparations

• Teas and Decoctions

A tea, or infusion, is made by pouring boiling water over finely chopped plant material (usually leaves and flowers). The mixture is allowed to stand for a period of time before straining. The usual ratio is 500 ml (1 pint) ofwater to 30 g (1 oz) plant material.

Adecoction is made by adding cold water to the plant material and then heating it to a boil. The mixture is allowed to simmer before cooling and straining. Decoctions are often made of roots, bark, and berries, which may require more forceful treatment than more fragile plant parts such as leaves and flowers.

The same proportions of water to plant material apply, but it is best to start with 800 ml (1½ pints) to allow for evaporation. Teas and decoctions may be consumed either hot or cold.

• Plant Juices

Freshly harvested plant parts can be pressed to release their juices. The shelf life of the expressed juice is usually extended by pasteurization or by rapid, ultra-high-temperature treatment. In addition, alcohol may be added as a preservative.

• Tinctures

A tincture is made by soaking the plant material in a solution of alcohol and water for a period of time followed by filtering. Tinctures are sold in liquid form and are useful for both concentrating and preserving an herb. They are made in different strengths that are expressed as ratios.

Traditionally, a ratio of 1 part herb to 5 or 10 parts liquid (1:5 or 1:10) has been used. These ratios represent 100 g (3½ oz) plant material in 500 ml (1 pint) of solvent, or 100 g plant material in 1000 ml (2 pints) solvent.

• Extracts

Extracts are concentrated preparations that can be in liquid, viscous, or powdered form. They are prepared from fresh or dried plant material by distillation, maceration (soaking then filtering), or percolation. The extraction liquid or solvent is chosen for its chemical properties, as it will selectively extract components in the plant that match those chemical properties.

Typical solvents include water-alcohol mixtures, glycerin (a colorless, odorless, syrupy, sweet liquid), oils, supercritical gases (carbon dioxide can be liquefied at certain temperatures and pressures), hexane, methylene chloride, acetone, and ethyl acetate.

Some or all of the liquid solvent can then be evaporated to make a dry extract, which can be easily placed into capsules or made into tablets. This is often accomplished by evaporating the liquid in the presence of a carrier such as cellulose, lactose, maltodextrose, or even dried plant material.

Again, ratios are used to describe the strength of the extract. Most crude plant materials have a content of roughly 20 percent extractable substances which corresponds to an herb to extract ratio of 5:1. If the extract is further purified, even greater ratios can be obtained.

However, this means that some components of the plant have been selected over other components. For example, the standardized ginkgo extracts, which are made in a multistep purification process, are highly purified extracts with an average ratio of 50:1.

This ratio means that 50 parts of plant material went into producing one part extract. Essentially the extract is a concentration of certain flavonoids and terpenes present in ginkgo leaves.

• Syrups

Medicinal syrups are viscous liquids that contain a minimum of 50 percent sugar, more typically 65 percent, added to a plant extract. This high concentration of sugar acts as a preservative.

• Oils

Oils can be produced by pressing or extracting plant materials such as seeds and fruits. Crude oils can be refined by distillation. Alternatively, medicinal oils can contain plant substances dissolved in oil. These oil-based extracts are typically used as salves or in other topical applications.

Formulations

• Tablets

Tablets are made by compressing powdered or granulated material. Besides the active ingredients, tablets may contain diluents, binders, lubricants, coloring, and flavoring agents. They also contain disintegrators that help the compressed tablet to dissolve when it comes in contact with water.

Tablets can be coated with sugar, dyes, fat, wax, or film-forming polymers. The function of the coating may be to extend the life of the tablet by protecting the active ingredients.

It also may be to control or delay the release of the active ingredient. Coated tablets may mask any unpleasant taste of the active ingredient and may make the tablet easier to swallow.

• Capsules

Hard gelatin capsules consist of a two-part cylindrical shell. They usually enclose plant material or dried extracts. Soft gelatin capsules are spherical, oval, oblong, or teardrop shaped and consist of a gelatin shell enclosing semisolid or liquid contents.

The composition of the capsule can be designed to control the release of the contents. For example, an enteric coating, which resists the acid in the stomach, will dissolve in the intestine when the pH rises above 7.

• Lozenges

Lozenges have a tabletlike appearance but differ in that they are not made by compression. They are molded or cut from a gummy mass. Lozenges are designed to release the active ingredient slowly in the mouth while being sucked or chewed. They are often made with sugar, gums, gelatin, and water.