Licorice Root: Traditional Use, Constituents and Evidence

Roughly 4,000 years of continuous medicinal use is a long time to be wrong about a plant , but it's also not the same thing as being right. Licorice root sits in that complicated middle ground that anyone who takes phytomedicine seriously has to reckon with: a plant with a genuinely interesting chemical profile, a dense historical record, and clinical evidence that, in most areas, still falls short of what we'd want to see.

My nan kept a jar of licorice root pieces on the shelf next to her chamomile and her elderflower tinctures. She'd been given them by a Greek neighbour in the 1960s who swore by them for "the chest." I never questioned it as a kid. Now I spend a lot of time reading the actual literature, and the honest answer is: some of that chemistry is genuinely fascinating, and some of the claims built on top of it are a long stretch.

A brief history worth knowing

Glycyrrhiza glabra (common licorice) and its close relative Glycyrrhiza uralensis (Chinese licorice) have appeared in Assyrian herbals, Egyptian tombs, traditional Chinese medicine formularies, Ayurvedic texts, and European pharmacopoeias going back centuries. The genus name comes from the Greek glykys (sweet) and rhiza (root) , the root is around 50 times sweeter than sucrose, which is partly why it travelled so well as a trade commodity and flavouring agent.

In Chinese medicine it appears as gancao and is one of the most frequently cited herbs in classical formulae, often described as a harmonising agent. In European herbalism, figures from Theophrastus through to Nicholas Culpeper wrote about its uses for respiratory and digestive applications. Whether those traditional frameworks map cleanly onto the mechanisms we now study in pharmacology is a separate and genuinely thorny question.

Key constituents

The chemistry is where licorice root earns its interest. The main bioactive groups are triterpenoid saponins, flavonoids, and a smaller set of coumarins and polysaccharides.

Glycyrrhizin is the dominant saponin and the compound most associated with the plant's distinctive sweetness. It's a prodrug of sorts: gut bacteria hydrolyse it to glycyrrhetic acid (also written as glycyrrhetinic acid), which has a longer biological half-life and is considered the pharmacologically active form. Glycyrrhizin and glycyrrhetic acid have been studied for their effects on cortisol metabolism , specifically, glycyrrhetic acid inhibits the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), which normally converts active cortisol to inactive cortisone in the kidney. That's the mechanism behind a real and well-documented safety concern I'll come back to.

Flavonoids in licorice include liquiritigenin, isoliquiritigenin, glabridin, and lichalcone A. These are structurally diverse and have been studied across a range of in vitro assays. Glabridin in particular has attracted attention for its antioxidant properties and its weak oestrogenic activity; it binds oestrogen receptors in cell models, though the relevance of that binding at typical dietary exposures is genuinely uncertain.

Some of these flavonoids also interact with pathways studied in cannabinoid pharmacology contexts. Glabridin and isoliquiritigenin have been examined in research touching on inflammatory signalling, some of which overlaps with pathways involving the endocannabinoid system. That doesn't mean licorice root is a cannabinoid, it isn't, but it's a useful reminder that plant chemistry rarely respects tidy category boundaries. The terpene content of licorice root is modest compared with plants like cannabis or lavender, though beta-caryophyllene has been identified as a minor constituent in some analyses.

The polysaccharides and other minor constituents round out a profile that is genuinely complex. Which is also part of why studying it is hard: isolating the contribution of any single compound in a whole-plant preparation is methodologically difficult, a challenge that applies across all of phytomedicine. The idea of a standardised extract; specifying a minimum percentage of glycyrrhizin or glabridin, is one way researchers try to manage that variability.

What the research actually shows

The short version is: preclinical evidence is extensive; quality clinical evidence is limited.

A substantial body of in vitro and animal research has examined licorice constituents across antioxidant, antimicrobial, antiviral (particularly glycyrrhizin against various enveloped viruses), and anti-inflammatory assay models. Some of this work is rigorous. The problem, and I say this as someone who finds the chemistry genuinely interesting; is that strong in vitro results routinely fail to translate to equivalent clinical outcomes. Cell culture and mouse models are hypotheses, not conclusions.

Human clinical trial data for licorice-derived compounds is scattered and often low-quality. A 2012 Cochrane-adjacent systematic review noted significant methodological heterogeneity across trials using licorice preparations. Sample sizes are small, standardisation of extracts is inconsistent, and blinding is often inadequate. The most studied clinical application has been in gastrointestinal contexts, particularly relating to Helicobacter pylori, where some trials have examined licorice-derived compounds as adjuncts. Results have been mixed and the evidence base does not currently support firm conclusions.

Intravenous glycyrrhizin preparations have been used in Japan for decades in hepatology contexts, that's a distinct clinical pathway with a different regulatory and evidence history from oral supplementation, and it would be misleading to conflate the two.

Safety: the issue that doesn't get enough airtime

Licorice root has a real, mechanism-based safety concern that sometimes gets buried under the promotional language you see on health blogs. Sustained high-dose consumption of glycyrrhizin, through either concentrated extracts or, historically, confectionery; has been associated with a syndrome of apparent mineralocorticoid excess: raised blood pressure, hypokalaemia (low potassium), and fluid retention.

The European Food Safety Authority (EFSA) has reviewed glycyrrhizin intake and identified 100 mg/day as a level above which adverse effects may occur in sensitive individuals, including those who are pregnant or have existing cardiovascular or renal conditions. The World Health Organisation's recommended maximum daily intake of glycyrrhizic acid is 100 mg, acknowledging this is likely to be exceeded by people consuming licorice confectionery at typical serving levels.

This matters in Australia because licorice root is available in various complementary medicine products. Under the Therapeutic Goods Act 1989, products listed on the Australian Register of Therapeutic Goods (ARTG), see our ARTG glossary entry, go through a listing pathway (ARTG Listed, prefix "AUST L") that relies on self-assessment of safety and evidence for low-level claims. The TGA does not independently assess listed products for efficacy before they reach shelves. That's not a scandal, it's the designed framework for complementary medicines; but consumers should understand it. Higher-risk therapeutic claims require the registered product pathway (AUST R), which involves TGA evaluation. The TGA's published guidelines for listed complementary medicines outline permitted indications and the standard of evidence required.

Deglycyrrhizinated licorice (DGL) is a processed form with most of the glycyrrhizin removed, which reduces but does not eliminate the safety concern profile. It's commonly used in products aimed at digestive applications. The bioavailability and pharmacokinetic profile of glycyrrhizin and glycyrrhetic acid is also relevant here, glycyrrhizin is poorly absorbed intact from the gut and requires bacterial conversion, meaning individual variation in gut microbiome composition likely affects how much active metabolite any given person produces. Our pharmacokinetics glossary covers those principles in more detail.

Australian regulatory context

Licorice root is not a scheduled substance under the Poisons Standard in the way that, say, kava is subject to import controls (kava remains under a complex regulatory framework involving personal importation limits and an ongoing approved pilot for licensed sales, licorice has no equivalent restriction). Standard over-the-counter complementary medicine rules apply.

For practitioners using licorice root in a clinical context, formulation quality varies considerably. Good Manufacturing Practice (GMP) certification is required for Australian ARTG-listed products and provides some assurance around consistency of the extract. Products sourced from outside the ARTG framework; including many unlisted herbal products sold online, carry no such assurance of standardisation or quality.

I'd argue, honestly, that the gap between how licorice root is marketed in the complementary medicine space and what the clinical evidence actually supports is wider than it should be. The chemistry is interesting enough to stand on its own without overclaiming. Researchers like those at the University of Adelaide's pharmacy faculty have contributed to phytochemical characterisation work on Glycyrrhiza species, that kind of careful constituent mapping is where the field needs to keep going, rather than racing ahead of the data.

Sources

• Listed Complementary Medicines: Evidence Guidelines; TGA (Therapeutic Goods Administration)
• Licorice Root: Background, Chemistry, Pharmacology, StatPearls, NCBI/NLM
• Scientific Opinion on the safety of glycyrrhizinic acid, EFSA Journal
• WHO Monographs on Selected Medicinal Plants, Vol. 1; World Health Organisation

, Naomi Ellison, Botanical & phytomedicine writer