Is green tea considered a medicine in Australia?

It depends on the form. Brewed green tea consumed as a food or beverage sits outside TGA jurisdiction. Products that make therapeutic claims — capsules, extracts, tinctures sold with health indications — must be listed or registered on the ARTG (Australian Register of Therapeutic Goods). Listed complementary medicines containing green tea extract can make only low-level 'permitted indications' as defined by the TGA, not disease treatment claims.

What is EGCG and why does it attract so much research attention?

Epigallocatechin gallate (EGCG) is the most abundant catechin in green tea and the most studied. It's a polyphenol with a structure that interacts with multiple biological targets in laboratory settings — enzyme inhibition, antioxidant reactions, and cellular signalling pathways have all been documented in vitro. The challenge is that EGCG has very poor oral bioavailability in humans, meaning the concentrations seen in cell studies are difficult to achieve in circulating blood from dietary intake.

Are high-dose green tea extract supplements safe?

This is an area where regulatory caution is warranted. The European Food Safety Authority's 2018 assessment flagged that EGCG intakes above 800 mg per day from supplements — not from brewed tea — were associated with signals of liver toxicity in pharmacovigilance data. The TGA maintains an adverse event reporting system for complementary medicines. Consumers considering high-dose green tea extract products should speak with a qualified health professional and check that any product they consider is listed on the ARTG.

How is green tea different from black or white tea?

All three come from Camellia sinensis but are processed differently. Green tea is minimally oxidised (heated shortly after picking to stop enzymatic oxidation), which preserves catechins like EGCG. Black tea undergoes full oxidation, converting catechins into theaflavins and thearubigins — different polyphenols with their own research literature. White tea is made from young buds with very minimal processing. Caffeine levels vary across types but the catechin profile differs substantially.

Does adding milk to green tea affect its constituents?

Possibly, though the evidence is mixed. Some research suggests that milk proteins (particularly caseins) can bind to catechins and reduce their bioaccessibility in the gut. This effect has been studied more in black tea than green tea. Temperature, steeping time, and what else you consume alongside the tea all influence how catechins are absorbed — it's a genuinely complicated pharmacokinetic picture.

Green Tea (Camellia sinensis): Traditional Use, Constituents and Evidence

By Naomi Ellison · 1 July 2026 · 7 min read

woman in white robe standing in front of sink

A plant that's been misunderstood twice over

My nan kept a row of old Fowler's jars on her kitchen bench in the Adelaide Hills, each one labelled in her particular cursive: rosemary, valerian, chamomile. Green tea never made the shelf because, in her view, it was simply a drink , not medicine. I've spent a fair bit of time since then reading the research and the history, and I reckon the truth sits somewhere more complicated than either camp would like.

Camellia sinensis is one of the most studied plant species on earth. It's also one of the most misrepresented, with a long tradition of cultural use on one side and a mountain of industry-funded clinical literature on the other. Getting to what the evidence actually shows , carefully, without overselling it , takes a bit of work.

Traditional use and botanical history

The earliest credible written record of tea as a consumed plant dates to the Chinese text Shennong Bencao Jing, compiled roughly in the first century CE, though oral tradition places its use much earlier. Tea cultivation spread through China's Yunnan province before moving to Japan (likely via Buddhist monks in the 8th–9th centuries CE), then across Southeast Asia and eventually to India under British colonial agricultural programmes in the 1830s.

Traditional Chinese and Japanese use of green tea was not primarily centred on the dried leaf as a supplement; it was a brewed preparation integrated into broader dietary patterns, ritual contexts, and in some traditions, a vehicle for other botanical preparations. Matcha, the powdered form used in Japanese tea ceremony, involves consuming the entire leaf rather than a water infusion, which changes the constituent intake considerably.

Ayurvedic traditions in South Asia documented tea somewhat later than Chinese sources, and use varied substantially across different schools of practice. The point is that "traditional use" here spans thousands of years, multiple cultures, and wildly different preparation methods, conflating them into a single claim about what the plant "does" is where a lot of popular writing goes wrong. This is a plant with a rich history as a phytomedicine; it doesn't need the history airbrushed to look more impressive than it is.

Key constituents

The primary phytochemical interest in Camellia sinensis centres on four main compound groups.

Catechins, a subclass of flavan-3-ols; make up the bulk of the polyphenol content in unoxidised (green) tea. The most studied is epigallocatechin gallate, usually written as EGCG. Other catechins present include epicatechin (EC), epigallocatechin (EGC), and epicatechin gallate (ECG). EGCG typically accounts for 50–80% of total catechin content in green tea, though this varies significantly with cultivar, growing altitude, harvest season, and processing. Black tea, which is fully oxidised, converts most catechins to theaflavins and thearubigins, chemically distinct compounds with their own emerging research profiles.

Caffeine is the most pharmacologically active constituent in terms of acute, well-established physiological effects. Green tea contains roughly 20–45 mg of caffeine per 200 mL brewed cup, depending on leaf grade and steep time. This is meaningfully less than most espresso preparations but comparable to some instant coffee preparations at lower concentrations. Caffeine's mechanism of action, primarily adenosine receptor antagonism; is well characterised.

L-theanine is an amino acid (a non-protein amino acid, to be precise) found almost exclusively in tea and one mushroom species. It crosses the blood-brain barrier and has been the subject of genuine neuroscientific interest. Studies in the NCBI literature describe effects on alpha-wave EEG activity, though the clinical significance of those findings remains contested.

Chlorophyll, volatile aromatic compounds, and minor alkaloids, including theophylline and theobromine in small quantities, round out the picture. The volatile aroma compounds are where green tea's sensory character lives: pyrazines, aldehydes, and a range of terpenoid-family molecules. If you've ever read about terpenes in other plant contexts, you'll recognise the structural families.

One thing that doesn't get discussed enough: constituent concentration in a brewed cup differs enormously from what ends up in a standardised extract capsule. The bioavailability of catechins from a hot water infusion is influenced by milk addition, temperature, steeping duration, and the food matrix at time of consumption. Catechins are notoriously poorly absorbed; oral bioavailability of EGCG in humans is typically reported below 1% in fasted states, with wide inter-individual variability.

The research landscape; and its limits

Let me be honest about what the clinical literature looks like. There is a large volume of in vitro (cell culture) work showing various effects of EGCG on biological pathways. There is a moderate body of animal studies. There is a smaller, but growing, body of human clinical trials, many of which are short-duration, use widely varying doses, and were funded by tea industry bodies. That last point matters. The Cochrane review methodology specifically flags industry funding as a source of bias risk, and it applies here.

The most-studied research areas include cardiovascular markers, glycaemic indices, and body composition. None of these are areas where I can make therapeutic claims here, nor should I, and nor should you read marketing materials that do. What I can say is that the mechanistic hypotheses are genuinely interesting from a biochemistry standpoint, and researchers like those at the Linus Pauling Institute at Oregon State University have published reasonably careful summaries of what's established versus speculative.

Pharmacokinetics is a recurring sticking point. Because catechins undergo significant first-pass metabolism in the gut and liver, the concentration that reaches systemic circulation from an oral dose is a fraction of what was consumed. Studies that dose animals via intraperitoneal injection and then extrapolate to humans drinking tea are not doing rigorous science, and there are unfortunately quite a few of them in the literature.

Green tea in Australian regulatory context

In Australia, Camellia sinensis preparations are regulated by the TGA. Products listed on the Australian Register of Therapeutic Goods (ARTG) as Listed medicines (AUST L or AUST L(A)) must comply with the TGA's permitted indications; a defined list of lower-level claims. Manufacturers cannot make claims that the product treats or prevents specific diseases without registered (AUST R) status, which requires far more extensive clinical evidence.

Green tea extract is included in the TGA's list of permitted ingredients for listed complementary medicines. This means it can appear in ARTG-listed products, but the listed status is based on a self-assessment of safety and quality, not independently verified efficacy. The TGA is clear about this distinction on its website, and consumers are entitled to know it.

High-dose green tea extract products, particularly those delivering concentrated EGCG above levels achievable from normal dietary consumption, have been associated with hepatotoxicity signals in international pharmacovigilance data. The European Food Safety Authority reviewed this in 2018 and concluded that EGCG intakes above 800 mg/day from supplements were associated with an increased risk of liver injury. The TGA has its own adverse event reporting system and has issued related guidance over the years. This doesn't mean a cup of green tea is dangerous; it means concentrated extract products sit in a different risk category than a daily brew.

Worth noting: kava (Piper methysticum) is another traditional plant with somewhat similar regulatory complexity in Australia; and kava's import controls (governed by the Therapeutic Goods Act 1989 and related import restrictions, with the regulatory framework updated in 2021–2022 to allow limited community import) are a useful comparison point for anyone interested in how Australia navigates plant medicines with traditional histories and hepatotoxicity concerns. Green tea doesn't face import restrictions, but the liver-related caution from regulatory bodies applies specifically to concentrated extracts, not dietary consumption.

What to make of all this

The short version is: Camellia sinensis is one of the most chemically complex plants in common human use, with a documented history stretching back over two millennia. Its constituents, particularly the catechins and L-theanine, have generated genuine scientific interest and are the subject of ongoing research. That research has real methodological limitations, and the gap between in vitro findings and human clinical outcomes is wide.

I'd argue that the biggest disservice done to green tea's actual botanical legacy is the rush to turn it into a supplement story. The traditional preparation; brewed leaves, consumed with attention, often as part of a broader dietary and social practice, is itself the interesting object. The isolated-EGCG-in-a-capsule version is a different thing entirely, and the evidence base for it is a lot thinner than the marketing suggests.

Anyway. My nan wasn't wrong to keep it in the kitchen. She just might have underestimated how much chemistry was in her cup.

Sources

, Naomi Ellison, Botanical & phytomedicine writer

Common questions

Is green tea considered a medicine in Australia?: It depends on the form. Brewed green tea consumed as a food or beverage sits outside TGA jurisdiction. Products that make therapeutic claims — capsules, extracts, tinctures sold with health indications — must be listed or registered on the ARTG (Australian Register of Therapeutic Goods). Listed complementary medicines containing green tea extract can make only low-level 'permitted indications' as defined by the TGA, not disease treatment claims.
What is EGCG and why does it attract so much research attention?: Epigallocatechin gallate (EGCG) is the most abundant catechin in green tea and the most studied. It's a polyphenol with a structure that interacts with multiple biological targets in laboratory settings — enzyme inhibition, antioxidant reactions, and cellular signalling pathways have all been documented in vitro. The challenge is that EGCG has very poor oral bioavailability in humans, meaning the concentrations seen in cell studies are difficult to achieve in circulating blood from dietary intake.
Are high-dose green tea extract supplements safe?: This is an area where regulatory caution is warranted. The European Food Safety Authority's 2018 assessment flagged that EGCG intakes above 800 mg per day from supplements — not from brewed tea — were associated with signals of liver toxicity in pharmacovigilance data. The TGA maintains an adverse event reporting system for complementary medicines. Consumers considering high-dose green tea extract products should speak with a qualified health professional and check that any product they consider is listed on the ARTG.
How is green tea different from black or white tea?: All three come from Camellia sinensis but are processed differently. Green tea is minimally oxidised (heated shortly after picking to stop enzymatic oxidation), which preserves catechins like EGCG. Black tea undergoes full oxidation, converting catechins into theaflavins and thearubigins — different polyphenols with their own research literature. White tea is made from young buds with very minimal processing. Caffeine levels vary across types but the catechin profile differs substantially.
Does adding milk to green tea affect its constituents?: Possibly, though the evidence is mixed. Some research suggests that milk proteins (particularly caseins) can bind to catechins and reduce their bioaccessibility in the gut. This effect has been studied more in black tea than green tea. Temperature, steeping time, and what else you consume alongside the tea all influence how catechins are absorbed — it's a genuinely complicated pharmacokinetic picture.