Green Tea Extract and the Liver: What the USP Review Found

By the Gelatide TeamLast updated November 4, 20269 min readSafety · Reviewed by Dr. Dean Tomlin

Tea and extract are different exposures

Green tea is one of the most studied drinks in the world, and a cup of it is not what this post is about. Brewed tea delivers its catechins, the family of plant compounds that includes EGCG, dissolved in a few hundred millilitres of water, usually sipped over a meal or a morning.

A green tea extract is a concentrate, made to deliver catechins in a small dose: a tablet, a capsule, a scoop or, in Gelatide’s case, a liquid drop. That changes how much can arrive at once, and how fast. NCCIH reports no safety concerns for green tea drunk as a beverage by adults, and notes that the uncommon cases of liver injury have involved green tea products, mainly extracts in tablet or capsule form. It also lists nausea, constipation, abdominal discomfort and raised blood pressure among the side effects of extract supplements.

What the USP review did

The United States Pharmacopeia sets public quality standards for medicines and supplements, and it reviews safety data for the ingredients it writes standards for. In 2020 a USP panel published a comprehensive review of the hepatotoxicity of green tea extracts in Toxicology Reports.

The panel looked first at the obvious suspects. Extracts can carry solvent residues, pesticide residues, pyrrolizidine alkaloids and metals, and any of those could in principle harm a liver. The review found no evidence that they were behind the cases. The problem traced back to the catechins themselves, EGCG above all.

It also found that catechin profiles vary a great deal with how an extract is made, so two products both called green tea extract can deliver quite different amounts.

The empty-stomach finding

The most practical finding concerns timing. Animal and human data showed that repeated bolus doses of extract taken while fasting significantly increase how much EGCG reaches the blood. The review suggested that the mechanisms that normally clear catechins on their first pass through the gut and liver become saturated when a concentrated dose arrives on an empty stomach.

In the toxicology studies the injury followed a hepatocellular pattern, meaning damage to the liver cells themselves. In the published case reports it was associated with EGCG intakes from 140 mg to about 1,000 mg a day, and susceptibility varied widely between people, possibly for genetic reasons. NCCIH puts a figure on one of those reasons: people with a particular variant of an immune-system gene appear especially susceptible, and between 5 and 15 percent of Americans carry it.

The caution USP now requires

On the strength of the review, USP added a cautionary labelling requirement to its standard for one form of the ingredient, powdered decaffeinated green tea extract. In substance it says:

• do not take it on an empty stomach, and take it with food;
• do not use it if you have a liver problem;
• stop and consult a healthcare practitioner if symptoms of liver trouble develop, such as abdominal pain, dark urine, or yellowing of the skin or eyes.

That wording applies to products made to that USP standard. The reasoning behind it applies to any concentrated green tea extract, which is why the same caution sits here and on the side effects page for Gelatide.

The warning signs, in plain words

The USP caution names three signs. They are uncommon, and most people who take green tea extract never see one; the point of knowing them is that the response is simple and immediate.

For clinicians, the NIH’s LiverTox monograph on green tea collects the published cases and the pattern of injury in detail.

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The caffeine that comes with it

The USP caution was written for a decaffeinated extract. Green tea leaf extract normally carries some caffeine, and guarana seed, another of the six in Gelatide, is a caffeine source in its own right.

That matters for two reasons. Caffeine is one of the reasons green tea extract shows any effect at all in the research, as the next section explains. And it adds its own cautions, from sleep to blood pressure to interactions with stimulants and some heart and asthma medicines, which the side effects page sets out in full.

Where a dropper sits in that range

The USP review gives a range, 140 mg to about 1,000 mg of EGCG a day, and it is fair to ask where a dropper of Gelatide sits in it. Start with the Supplement Facts panel on the bottle and what it declares for a serving. How much of any green tea extract is EGCG depends on how it is standardised, so the extract figure is the start of the answer rather than all of it.

Either way, two habits the review points to cost nothing: take the drops with food, and do not stack them with other green tea extract products or concentrated tea supplements on the same day, because their catechins add up.

What green tea extract does offer

Balance matters. Green tea extract is on the label for a reason, and its research is the deepest of the six ingredients. A 2010 meta-analysis of 15 trials and 1,243 people found catechins taken with caffeine lowered body weight by about 1.38 kg and waist by about 1.93 cm, while catechins without caffeine showed no benefit on any measure; the authors called the effect modest at best. An earlier 2009 meta-analysis of 11 studies put the average at about 1.31 kg. The average was smaller in people who already drank a lot of caffeine, though that difference fell short of significance.

Those are small effects, measured for weight rather than digestion, and tied to caffeine, which in Gelatide comes from guarana and normally from the green tea itself. They are the reason the ingredient is there; the USP review is the reason to take it sensibly. The ingredients page sets green tea beside the other five.

If you already drink green tea

You do not have to give up the cup. NCCIH reports no safety concerns for green tea drunk as a beverage by adults, and the USP review is about concentrated extract, not the drink. What is worth a thought is the caffeine: a pot of green tea, a coffee and a caffeine-bearing drop in the same morning add up.

The combination to avoid is a second extract. A green tea capsule, a fat-metabolism powder with green tea in it and a green tea drop on the same day stack concentrated catechins from three labels, and none of them can tell you the total.

Medicines worth a question

Green tea can also change how some medicines behave. NCCIH notes that green tea at high doses has been shown to lower blood levels of nadolol, a beta-blocker used for high blood pressure, and so to reduce how well it works. That is one documented example rather than a complete list.

Add the caffeine that guarana and green tea normally bring, and the list of medicines worth a question before the first dropper grows: stimulants, certain antibiotics, asthma medicines and heart medicines among them. A pharmacist with the bottle in hand can check your own list in a few minutes, which is quicker than any amount of reading.

A sensible routine

1. With food. Breakfast or another meal, every time.
2. Within the label. One or two full droppers a day, never more.
3. One green tea source. No other green tea extract product on the same day.
4. Liver first. With a liver condition, or medicine processed by the liver, ask a pharmacist before the first dropper.
5. Stop at a sign. Abdominal pain, dark urine or yellowing skin or eyes: stop, and get checked.

The bottom line

Concentrated green tea extract has a rare but real link to liver injury, driven by EGCG, made more likely by large doses on an empty stomach, and very uneven between people. Gelatide names green tea leaf extract among its six ingredients, so the same habits apply to it: take the drops with food, keep to the label, avoid doubling up on green tea products, and know the three warning signs.