Standardisation of Botanical Extracts

The number on the label is doing a lot of work

Forty-five percent polyphenols. Twenty percent hypericin. Eight percent withanolides. These figures appear on botanical extract labels constantly, and most people read them the way I read cryptic crossword clues , confidently, then slowly realise there's a whole second layer of meaning they missed.

Standardisation in botanical extracts is a manufacturing and analytical concept, not a therapeutic promise. It describes the process of adjusting a raw plant extract so that a particular chemical constituent , the marker compound , appears at a consistent, specified concentration from batch to batch. That's the short version. The long version involves a lot of arguments between analytical chemists and pharmacognosists about what a marker compound actually tells you.

Worth keeping that tension in mind as we go.

Why plants resist uniformity

A plant is not a pharmaceutical factory. The same Cannabis sativa cultivar grown in two different Queensland paddocks can produce meaningfully different cannabinoid profiles depending on soil mineral content, light hours, temperature variation and harvest timing. This is not a flaw in the plant; it is biology doing what biology does. But it creates a real problem for anyone trying to formulate a consistent extract-based product.

Secondary metabolites; the class that includes cannabinoids, terpenes, alkaloids, flavonoids, are biosynthesised partly in response to environmental stress. A plant under UV or pathogen pressure may up-regulate certain pathways. One grown in more sheltered conditions may not. The result is that two samples of ostensibly the same botanical material can differ quite substantially in the concentration of the very compounds researchers find most interesting.

This variability cascades directly into pharmacokinetics. If a researcher gives a fixed gram-weight dose of an unstandardised herb extract to participants in a study, they may effectively be giving different biochemical inputs to each participant. Controlling for that in clinical trial design is genuinely difficult, and it is one reason why botanical medicine research is harder to compare across studies than single-molecule pharmaceutical research.

What standardisation actually involves

The technical process has a few distinct stages. First, the raw plant material is extracted, using a solvent such as ethanol, CO₂, or water, depending on the target compounds and the desired extract type. The crude extract is then assayed, typically by high-performance liquid chromatography (HPLC), to determine the actual concentration of the marker compound present.

If the marker concentration is lower than the target specification, the extract is concentrated. If it is higher, it is blended ("cut") with additional carrier material or with a weaker batch to bring it down. The final extract is re-assayed to confirm the stated percentage. This is the adjustment step that earns the word "standardised."

Good Manufacturing Practice; GMP, frameworks govern how this process is documented, validated and quality-controlled. In Australia, any botanical extract that reaches the market as a listed or registered medicine must be manufactured in compliance with GMP requirements overseen by the Therapeutic Goods Administration (TGA) and, where applicable, listed on the ARTG. The TGA's GMP guidance for complementary medicines specifically addresses extract characterisation and batch consistency requirements. See the Good Manufacturing Practice glossary entry for more on what that framework covers.

Marker compounds versus active compounds, a distinction that matters

Here is where the analytical chemists and the pharmacognosists start to disagree, and honestly I find this the most interesting part of the whole field.

A marker compound is whatever the manufacturer has chosen (or been directed by a pharmacopoeia) to measure as the proxy for quality. The assumption baked into this choice is that the marker correlates with; or directly represents, the pharmacologically active fraction. Sometimes that assumption holds. Often it is an approximation. And in complex botanical matrices, it can be quite misleading.

Take a full-spectrum cannabis extract. Standardising to a stated concentration of cannabidiol tells you something about CBD content, but it tells you nothing about the dozens of minor cannabinoids, the terpenes, the flavonoids, or the relative ratios of those constituents. A product standardised to a fixed CBD percentage may have vastly different profiles of compounds like beta-caryophyllene, myrcene, or linalool across batches, and researchers studying potential entourage interactions (see our Entourage Effect page for background) argue those ratios are anything but irrelevant.

The broader point is that standardisation to a single marker is a pragmatic industrial solution to variability, not a full characterisation of the extract's biochemical complexity. A standardised extract and a fully characterised extract are not the same thing, even though those terms sometimes get used interchangeably in marketing material.

Fingerprinting as an alternative approach

Some manufacturers and research groups use phytochemical fingerprinting rather than, or alongside, single-marker standardisation. The idea is to produce a chromatographic or spectroscopic "fingerprint" of the whole extract; a pattern that can be compared batch to batch to ensure the entire chemical profile is consistent, not just one constituent.

This approach aligns more closely with the concept of phytomedicine as a discipline, which tends to take seriously the idea that plant extracts are biochemically complex systems. A fingerprint can reveal if a minor constituent has shifted even when the marker compound reads correctly, something marker-only standardisation would miss entirely.

The practical challenge is that fingerprinting requires more sophisticated analytical infrastructure, and regulators have historically found it harder to set pass/fail specifications on a pattern than on a number. That gap is narrowing. The European Pharmacopoeia has moved toward fingerprint-based identity testing for a number of botanicals, and the TGA's guidance is tracking that direction for certain categories.

How this connects to bioavailability

Standardisation affects more than batch-to-batch consistency. It interacts directly with bioavailability, the fraction of a compound that reaches systemic circulation in an active form.

A concentrated extract in a particular delivery vehicle (say, an oil-based softgel) may have very different absorption kinetics than a water-extract standardised to the same marker percentage. Fat-soluble compounds; cannabinoids are a clear example, are heavily influenced by the lipid environment they're delivered in. And the first-pass metabolism effect, where orally delivered compounds are substantially modified before reaching systemic circulation, can differ depending on what else is present in the extract matrix.

I was reading through a 2021 paper in the Journal of Natural Products on piperine-mediated bioavailability enhancement last month, found it tucked in a secondhand pharmacognosy textbook I picked up at a Paddington shop, which is its own small story; and the key point it kept circling back to was that the excipient matrix around a standardised extract can shift absolute bioavailability more dramatically than the standardisation ratio itself. The number on the label describes the extract; it doesn't describe what the body actually receives.

The regulatory picture in Australia

For botanical products in the Australian market, the TGA regulates under the Therapeutic Goods Act 1989. Listed medicines (ARTG "L" numbers) are largely self-assessed by sponsors against TGA-approved indications and permitted ingredients, they don't require pre-market efficacy review, but they must meet ingredient and GMP standards. Registered medicines require a higher level of evidence review.

For prescription-only botanical products, certain cannabis-derived medicines, for instance; the regulatory pathway is more involved. Products containing tetrahydrocannabinol above threshold concentrations are Schedule 8 controlled drugs under the Poisons Standard; CBD products above 2% concentration are Schedule 4 prescription-only. Access pathways include the Special Access Scheme and the Authorised Prescriber framework. None of that changes regardless of how rigorously an extract is standardised.

The point for pharmacology is that regulatory status follows the compound and its concentration, not the manufacturing method. A beautifully standardised, GMP-certified extract of a Schedule 8 substance is still a Schedule 8 substance.

Where the field is heading

My honest view, and I'll own this as an opinion, is that the industry's current obsession with single-marker standardisation numbers has run somewhat ahead of the underlying science. It gives consumers and practitioners a reassuring precision that the analytical reality doesn't always support. A well-fingerprinted, fully characterised extract with documented batch consistency is worth considerably more, scientifically speaking, than a single bold percentage claim on a front panel.

That said, standardisation is still far better than no characterisation at all, which was the norm in botanical medicine well into the twentieth century. The field is moving, slowly, toward multi-constituent characterisation as analytical costs drop and regulatory frameworks catch up. That's the right direction.

Sources

• Guidance on Complementary Medicines Evidence Requirements; Therapeutic Goods Administration (TGA)
• Challenges in Standardisation of Herbal Medicines, NCBI / PMC
• Quality Control Methods for Herbal Medicines, NCBI / PMC
• Manufacturing Principles for Medicinal Plants; Therapeutic Goods Administration (TGA)

, Tom Whitfield, Health librarian, references & fact-checking