In order to obtain beneficial phytochemicals from selected medicinal herbs, numerous extraction methods have evolved over the centuries. 

As a result, multiple delivery forms and extract ratios have developed. Our modern dispensaries reflect this, with shelves revealing an array of liquid herbal extracts in different ratios, tablets and in some cases, dried herbs for decoctions.

Versatility and flexibility are key to managing individual cases and as modern herbalists mixing traditional evidence with current research, the ability to calculate appropriate dosing and understanding how this translates between dried herb equivalents and liquid extract ratios is valuable knowledge.

Below we review important tips for understanding extract ratios and how to calculate dried herb equivalents.

Traditional Medicine Meets Modern Science

Traditional methods of herbal medicine preparation included the use of Infusions and Decoctions.²

Modern technology has since seen the development of herbal quality control through the creation of sensitive testing parameters (High Performance Liquid Chromatography (HPLC) and Mass Spectrometry (MS) which has continued to evolve the prescription of herbal medicines. Researchers have found a combination of water and ethanol to be a highly efficient solvent due to its ability to extract a wide variety of plant constituents and improve the stability of the herbal medicine. The optimal ratio of ethanol to water must be carefully determined to maximise the therapeutic activity of each specific herbal liquid and will depend on the type of active constituents contained within the herb. Below are some examples of herbs which need to be prepared in a specific percentage of ethanol to extract their key constituents.

Infusions: involves boiling water being poured over a particular quantity of finely cut or chopped plant parts (leaves, stems, flowers, roots, or fruits) for several minutes. The mixture can be consumed once the herb has been adequately infused in the water. Decoctions: involves the prolonged and more thorough boiling and soaking (‘‘steeping’’) of harder plant parts such as bark, seeds, or uncut roots.2

Ethanol Percentages for Specific Herbal Constituents

• 55% ethanol is optimal for chamomile flower (Matricaria chamomilla) to extract the essential oil and flavonoids.³
• Approximately 60% ethanol is a suitable solvent to extract most saponins.³
• Alkylamides, the important active constituent that produces the tingling sensation of good-quality echinacea root, are best extracted at higher ethanol percentages (60%).³
• Ginger (Zingiber officinale) is best extracted with 90% ethanol, otherwise poor-quality extracts containing low quantities of the pungent principles (a consitutient of the oleoresin) result.³

Ethanol percentage guidelines recommended to optimise the activity of the final liquid:

• 23%: water-soluble constituents such as mucilage, tannins, and some glycosides³
• 45–60%: essential oils, alkaloids, most saponins and some glycosides³
• 90%: resins and oleoresins³

Important note: Ethanol is not a suitable solvent for herbs containing highly water-soluble constituents such as mucilage. Slippery elm and Psyllium are best administered in powder form and mixed in water.³

Extract Equivalents & Dosage Calculations

Multiple dosage forms and extract ratios are now common in herbal medicine. Therefore, it is essential that clinicians can convert between herbal liquid extract and dry herb equivalent, and vice-versa. This process allows clinicians to quickly and accurately convert extract ratios to determine the dried herb equivalent of their prescriptions.³

Conversion ratios:

Herbal extracts are expressed as a ratio. This ratio reveals the amount of dried herb used to the amount of liquid produced. This is known as the herb extract ratio.⁴

For example

Weight of dried herb : Volume of the extract

1:1 = 1kg of dried herb was used to make 1L of liquid extract.

* Do note that a 1:1 is not necessarily the strongest extraction compared to other extract ratios. In order to ensure the optimal extraction of specific phytochemicals, different amounts of water and ethanol are required (see ethanol percentages above). As such, the extract ratio does not reflect the active constituents present in the final volume produced.

Conversion ratios depend on the extract ratio used in the specific herbal liquid. For example a 1:1 liquid (such as turmeric) contains 1 part herb to 1 part liquid, therefore the dried herb equivalent of herb in grams is the same amount of liquid you use in mL (5mL of liquid = 5g dried herb equivalent). Most MediHerb® liquids use a 1:2 extract ratio, this means for 1 part herb there are 2 parts liquid. In these circumstances 1mL of herbal liquid will be the equivalent to 500mg dried herb equivalent as shown in table 2. 

Table 1. Liquid Extract Ratios 

Table 2. Liquid and Dried Herb Equivalents

Finding the right Equation for your percolation

There are 2 key points to remember when calculating conversions:

• Dried herb to extract – divide
• Extract to dried herb – multiply

Clinical Examples:

Included below are some examples of calculations required for various herb extract ratios.

MediHerb® Chaste Tree tablets (1:2 extract)

• 1 tablet is equivalent to 500 mg of chaste tree, therefore 1 mL of chaste tree 1:2 will be equivalent to 500 mg of dried herb.
• For 1:2 extracts (1,000 mL ÷ 2 = 500mg dried herb)

Calculation

• X (dry herb quantity) = 500 mg
• Y (extract quantity) = unknown
• Extract ratio: 1:2 (or 1/2)

Equation: Divide the dry weight by the extract ratio (500 mg (0.500) divided by 1/2 (0.5) = 1 mL)

MediHerb® Golden Seal tablets (1:3 extract)

• 1 tablet is equivalent to 500 mg of golden seal. 1 mL of golden seal 1:3 extract is the equivalent to 333g dried herb, therefore 1.5 mL of golden seal 1:3 will be equivalent to 500 mg of dried herb.
• For 1:3 extracts (1,000 mL ÷ 3 = 333 mg dried herb)

Calculation

• X (dry herb quantity) = 500 mg
• Y (extract quantity) = unknown
• Extract ratio: 1:3 (or 1/3)

Equation: Divide the dry weight by the extract ratio (500 mg (0.500) divided by 1/3 (0.33) = 1.5 mL)

MediHerb® Ginkgo Forte tablets (2:1 extract)

• 1 tablet is equivalent to 3.0 g of ginkgo. 1 mL of ginkgo 2:1 extract is the equivalent to 2g of dried herb, therefore 1.5 mL of ginkgo biloba 2:1 will be equivalent liquid to 3.0 g of dried herb.
• For 2:1 extracts (1,000 mL x 2 = 2,000 mg dried herb)

Calculation

• X (dry herb quantity) = 3 g
• Y (extract quantity) = unknown
• Extract ratio: 2:1 (or 2/1)

Equation: Divide the dry weight by the extract ratio (3 g divided by 2/1 (2) = 1.5 mL)

Conversions of Common MediHerb® Products

A quick reference guide which focuses on the amount of liquid extract required to obtain the equivalent dose found in 1 MediHerb® tablet of the same herb is provided below in table 3.

Table 3. A Quick Reference Guide in converting MediHerb® Liquids and Tablets.

Conclusion

Modern technology has seen the prescription of herbal medicines evolve. With the wide array of dosage forms and extract ratios available to the modern herbalist, as well as the blending of traditional and evidence-based medicine, it is essential that clinicians are proficient in converting between herbal liquid extracts and dry herb equivalents. It is also important to understand that extract ratios may not always determine “strength” and that our complex phytochemicals require certain amounts of water and ethanol for optimal extraction. In this way, we can ensure our patients receive the correct therapeutic dose in a form that inspires compliance, while also being able to confidently translate an ancient art form to modern times.

References

1. Djordjevic SM. From medicinal plant raw material to herbal remedies. Aromatic and Medicinal Plants: Back to Nature. 2017 Mar 15:269-88.
2. Halberstein RA. Medicinal plants: historical and cross-cultural usage patterns. Annals of epidemiology. 2005 Oct 1;15(9):686-99.
3. Morgan M. Ethanol in Herbal Medicine. A Phytotherapist’s Persepctive. 2009; No.129. Available from: http://mediherb.com.au
4. Dosage calculations & extract equivalency in herbal medicine [Internet]. Sydney: Ian Breakspear [cited 2020 Jan 30]. Available from: https://ianbreakspear.com.au/2014/09/14/dosage-calculations-extract-equivalency-in-herbal-medicine/