Standardization and Marker Compounds for Herbs
What "standardized to" means on a herbal label, what a marker compound is and is not, and what studies found when they compared labels with measured contents.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read herb safety and interactions before you use anything on this page.
The question: does "standardized" mean the product is better?
Not on its own. In the research literature, standardization concerns the content of one or more active constituents and marker compounds in a herbal material. [1] NCCIH cautions that a manufacturer's use of the term "standardized" (or "verified" or "certified") does not necessarily guarantee product quality or consistency. [2]How the sources define the terms
- Herbal preparation. The EMA describes herbal preparations as products of treatments such as extraction, distillation, expression, fractionation, purification, concentration or fermentation. [3]
- Standardization. A 2012 review states that standardization guarantees the content of one or more active constituents and marker compounds. [1] Treat that as the ideal the term aims at, not as a promise every product on a shelf meets, as the findings below show.
- Why batches vary. The same review notes that the plant environment and genetic factors could significantly affect the biochemical components of a plant extract. [1]
- Extract details in official texts. An EU monograph entry can state an extract type, an extract ratio and the extraction solvent, for example "Soft extract (DER 114-222:1), extraction solvent: chloroform". [4] For a plain-language guide see standardized herbal extracts explained.
What studies found when they measured products
| Question | What the source found | Strength of evidence |
|---|---|---|
| Do St John's wort products contain the amount of marker compounds on the label? | Of 54 products bought in Canada and the US, label claim varied from 0% to 108.62% for capsules, and only two products were within 10% of their label claim. [5] The authors still call standardization an important step for batch-to-batch consistency. [5] | Small survey from 2003; products have changed since |
| Do milk thistle products match their silymarin label? | In 26 products from the US and Czech markets (2016-2017), large differences in silymarin content were found, often contrary to what manufacturers stated, and substantial differences between batches. [6] NCCIH reports similar findings. [7] | One study of one herb; small sample |
| Do curcumin products contain the same amount of curcumin? | NCCIH says oral curcumin products vary in how much curcumin they actually contain, which makes the evidence hard to compare. [8] | Agency summary |
What a marker percentage can and cannot tell you
A marker percentage is a statement about how much of one compound is present. Whether that compound explains any effect is a separate question that research has to answer, and a percentage does not show which other plant substances are present or whether a study's result applies to your product. NCCIH notes products you buy may differ in important ways from products tested in studies. [2]Proper evidence not found: we did not find, in the sources we read, a head-to-head comparison showing that products with a higher marker percentage give better health outcomes. We searched PubMed for reviews of herbal standardization and marker compounds and read the abstracts listed above. Our reading of the 2003 and 2012 papers is limited to their abstracts.
Frequently asked questions
What is a marker compound?
The sources we read do not give a one-line definition. In the St John's wort study, hypericin and pseudohypericin were the compounds measured against the label claim. [5] A marker is something measured; it is not proof of benefit.
Are standardized extracts safer?
The sources we read do not say so. NCCIH says "standardized" does not necessarily guarantee quality or consistency. [2]
Why do two products with the same herb give different results?
Plant environment and genetics can change an extract's biochemistry. [1] Products also differ from batch to batch, as measured in milk thistle. [6]
What does a ratio like 10:1 on an extract mean?
An EU monograph writes extract ratios in the form "DER 114-222:1" alongside the solvent. [4] For a plain explanation see extract ratios explained.
Does the preparation change what a study means?
Yes. The EMA notes that different preparations may exert different actions and in some circumstances may have a different safety profile. [9]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask
References
- Garg V, Dhar VJ, Sharma A, Dutt R. Facts about standardization of herbal medicine: a review. Zhong Xi Yi Jie He Xue Bao. 2012;10(10):1077-1083. PMID 23073189. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH, US). Using Dietary Supplements Wisely. Page last updated January 2019. Read 2026-10-23.
- European Medicines Agency. Herbal preparations (glossary). Read 2026-10-23.
- European Medicines Agency, Committee on Herbal Medicinal Products. European Union herbal monograph on Prunus africana (Hook f.) Kalkm., cortex, EMA/HMPC/680626/2013. Dated 12 July 2016. Read 2026-10-23.
- Analysis of the hypericin and pseudohypericin content of commercially available St John's Wort preparations. Canadian Journal of Clinical Pharmacology 2003;10(3):114-118. PMID 14506510. Read 2026-10-23.
- Fenclova M, Novakova A, Viktorova J, et al. Poor chemical and microbiological quality of the commercial milk thistle-based dietary supplements may account for their reported unsatisfactory and non-reproducible clinical outcomes. Scientific Reports. 2019;9:11118. PMID 31366891. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH, US). Milk Thistle: Usefulness and Safety. Page last updated February 2025. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH, US). Turmeric: Usefulness and Safety. Page last updated April 2025. Read 2026-10-23.
- European Medicines Agency, Committee on Herbal Medicinal Products. Glossary on herbal teas, EMA/HMPC/5829/2010 Rev.1. Dated 15 July 2010. Read 2026-10-23.