Green Tea Extract Uses, Benefits, Dosages, Side Effects & Interactions
Green tea extract is made from the leaves of the Camellia sinensis plant. In Japan and China, tea has been used for thousands of years as a beverage and herbal medicine.
Green tea has been used traditionally for increasing energy, enhancing mental alertness, improving digestion, and relieving headache.
In Ayurvedic and traditional Chinese medicine (TCM), this tea has been used to enhance wound healing, slow down bleeding, promote cognitive function, and improve body temperature regulation. 
Green tea extract supplements are commonly used for weight loss, mood balance, physical performance, anti-oxidant protection, immune support, anti-aging and as a nootropic aid. It is a source of caffeine and has been shown to boost metabolism and stimulate fat burning. As a source of the amino acid L-theanine, green tea extract also demonstrates positive effects on stress and emotional balance.
Green tea is made from the Camellia sinensis plant, an evergreen shrub/small tree.
Cultivators usually keep this plant trimmed down to about 6 feet in height so that its leaves can be more easily harvested.
Camellia sinensis leaves develop white hairs on their undersides, and grow up to 6 inches in length, and up to 2 inches in width. The leaves are said to most desirable for tea making when they are young, tender, and light-green in color. 
As the leaves mature, they become darker green, develop a bolder taste, and have a different chemical composition with different pharmacological effects then younger leaves. 
Seeds from C. sinensis are used to extract essential oil. Green tea oil is not the same as tea tree oil, which comes from an entirely different plant (Melaleuca alternifolia). 
The National Center for Complementary and Integrative Health (NCCIH) states that green, black, and oolong teas all come from the same plant. They differ only in preparation methods. 
According to The Tea Spot, “The distinguishing factor that determines whether a tea plant will become white, green, oolong, or black tea is oxidation.” 
After the leaves are harvested from the trees, they are processed by drying, withering, rolling and heat-treating. This imitates the process of oxidation.
The Tea Spot explains that, “A black tea is fully oxidized, causing it to turn black, while a white tea is barely oxidized at all, thus retaining its soft, silvery down.” 
Green tea is said to contain only about 1% caffeine, as compared to roughly 4% in black tea. Because of that, it is often used as a calming, quieting tea and not a stimulating, energizing drink. 
Chinese green tea is said to contain about 33 mg of caffeine per 8-ounce serving, and Japanese tea is said to provide 28 mg per cup. 
One method for preparing green tea is to place the leaves in purified water and gently boil them for 3 minutes. The leaves are strained out and the tea is consumed. 
How Does Green Tea Extract Work?
Green tea leaf extracts contain various phytonutrients (plant chemicals) that have health-boosting properties. This tea is known to contain significant amounts of antioxidant compounds called polyphenols. 
The University of Michigan Medical Center (UMM) states that the polyphenol compounds in green tea may have more potent antioxidant effects than ascorbic acid (vitamin C). These same compounds are also responsible for the bitter flavor of tea. 
The polyphenols in green tea leaves are classified as catechins. There are six primary catechins found in the leaves:
- Epicatechin gallate
- Epigallocatechin gallate (EGCG)
- Gallocatechin 
EGCG is the constituent of green tea that is most active in the human body and has been studied most extensively.
The tea leaves also contain stimulant alkaloids like caffeine, theophylline and theobromine. This extract also contains an amino acid called L-theanine, which is being studied for possible CNS (central nervous system) calming effects. 
Uses for Green Tea Extract
The Natural Medicines Comprehensive Database (NMCD) states that people use green tea extract orally for various purposes. Some of these uses include:
- Cardiovascular disease
- Chronic fatigue syndrome (CFS)
- Enhancing cognitive performance and mental alertness
- Human papillomavirus (HPV)
- Hypotension (low blood pressure)
- Non-alcoholic fatty liver disease (NAFLD)
- Stomach disorders like diarrhea and vomiting
- Ulcerative colitis 
The NMCD reports that green tea extract is also used for depression, weight loss, osteoporosis, headache, and sunburn.
It is also used for genital warts, perianal warts, cervical dysplasia, Crohn’s disease, Parkinson’s disease, dental caries/cavities, kidney stones, and skin damage. 
Green tea is also of interest to researchers for its potential anticancer effects. It has been studied for breast cancer, cervical cancer, prostate cancer, colon cancer, gastric cancer, liver cancer, lung cancer, leukemia, and skin cancer related to ultraviolet (UV) radiation. 
Applied topically, it is used:
- As a chewable candy for gingivitis
- As a compress for tired eyes and headache
- As a poultice for under-eye bags
- As a wash for athlete’s foot
- As a wash for sunburn
- To stop tooth socket bleeding 
Green Tea Extract Health Benefits
The NMCD rates green tea as Likely Effective for genital warts and hyperlipidemia (high blood lipid (fat) levels). 
Green tea is rated by the NMCD as Possibly Effective for cervical dysplasia, coronary artery disease (CAD), endometrial cancer, hypertension (high blood pressure), hypotension, oral leukoplakia (white patches in the mouth), ovarian cancer, and Parkinson’s disease. 
Clinical research suggests that this herbal extract may benefit various other health disorders. Some conditions where promising results have been observed in preliminary research trials include:
- Breast cancer
- Cardiovascular disease
- Esophageal cancer
- Mental alertness
- Prostate cancer
- Weight loss 
For these conditions, the clinical research is limited, and sometimes conflicting results exist. More research is needed to determine the therapeutic efficacy of green tea extract for these and any other conditions.
Green tea extract is regulated as a dietary supplement in the United States. The FDA has not approved this plant as a drug to prevent or treat any medical conditions.
Heart Health & Cardiovascular Disease
Research from population studies suggests that people who consume tea regularly might have better measures of heart health and lower risk of death from cardiovascular disease.
Epidemiological studies show that general tea consumption is correlated with a lower prevalence of ischemic heart disease. However, it is not known whether this effect is stronger with consumption of black tea or green tea. 
In one large human trial evaluating the link between tea drinking and heart health, 40,000 Japanese men and women between 40 and 70 years of age were monitored for 11 years.
The results showed that drinking at least 5 cups of green tea daily significantly reduced risk of mortality from all causes, but especially from cardiovascular disease. This was in comparison to those who drank less than 1 cup of tea daily. 
The polyphenol catechins in green tea extract are believed to support cellular health in general, but especially the cells of the heart and blood vessels. 
In 2011, a meta-review found that routine consumption of green tea was associated with modest yet significant reductions in low density lipoprotein cholesterol (LDL-C). 
LDL-C is considered to be the “bad” type of cholesterol because it contributes to the formation of arterial plaques which can lead to atherosclerosis (“hardening” and narrowing of the arteries due to plaque) and other cardiovascular disease.
According to the American Heart Association, drinking green tea regularly is associated with reduced risk for stroke. Japanese researchers also found that adding the tea to your daily diet may help to reduce risk for stroke. 
At this time the research has largely been positive, with population studies showing benefits for cardiovascular health associated with green tea consumption. The NMCD rates green tea as Possibly Effective for cardiovascular disease.
However more research is needed to determine the therapeutic efficacy of green tea for general heart health. The FDA has not approved this supplement as a drug to prevent or treat cardiovascular disease.
If you are interested in taking green tea extract for cardiovascular health then you should talk about it with your cardiologist or other primary health care provider.
There are side effects and interactions possible that you should be aware of before beginning to use green tea, especially if you have existing cardiovascular disease.
Green Tea for Cancer
The polyphenol catechins in green tea have been observed in in vitro (cultured cell) and animal studies to have various anticancer effects.
Researchers have observed antioxidant effects and antimutagenic effects (prevent mutations). Compounds in green tea has also been found to inhibit tumor cell proliferation and induce cancer cell apoptosis (cell death). 
The National Cancer Institute states that tea polyphenols are known to slow down tumor growth in cells studies and in animal research. This supplement may also provide protection to skin cells against UVB ultraviolet radiation. 
The NMCD reports that in humans, green tea has been observed to reduce damage done to DNA in lymphocytes, possibly through antioxidant activity and the activity of DNA repair enzymes. 
In some countries where people generally consume a lot of tea, overall cancer rates seem to be lower. However, there is no way to attribute those effects to tea drinking alone.
Various other factors may contribute such as diet, physical activity levels, exposure to toxins, and more. 
According to Medical News Today (MNT), in human research trials green tea extract has shown positive impacts on breast, bladder, colorectal, ovarian, throat, liver, lung, prostate, skin, and stomach cancer. 
It is hypothesized that the high levels of catechins in the tea are responsible for the anticancer effects seen in these trials. However, the precise mechanisms of action involved are still being investigated. 
While there have been many studies showing positive benefits, various other studies have not found any benefits for cancer prevention or recurrence from using green tea extract. 
The US FDA states that, currently, there is not enough reliable evidence that substantiates claims of reduced cancer risk from consuming green tea.  More research is still needed to determine the therapeutic efficacy for cancer.
If you are interested in learning more about green tea for cancer then it is best to discuss supplementation with your doctor or oncologist beforehand.
Green tea extract has been studied in a wide range of additional health conditions including diabetes, cognitive function, and weight loss.
While some of the results have been positive, there is conflicting evidence as well. More research is required in all of these uses to determine therapeutic efficacy
Green tea consumption has been studied for both type 2 diabetes prevention and treatment. Currently the results are unclear.
Some epidemiological research has shown that Japanese adults who consume at least 6 cups of tea per day have a 33% lower risk for developing diabetes compared to people who consume one cup or fewer per day. 
Clinical research has also shown that drinking three cups of green tea per day for 14 weeks does not improve fasting blood glucose levels, which may indicate that it does not affect diabetes development. 
While some meta-analyses data shows that fasting blood glucose levels are reduced in type 2 diabetics given green tea extract compared to a control, other studies have reported no reductions in this measure. 
More research is needed to determine how green tea affects blood sugar levels and diabetes.
In one meta-assessment, 21 research studies were reviewed examining the effects of green tea for cognition, mood, and brain function.
The researchers report that, “Green tea influences psychopathological symptoms (e.g. reduction of anxiety), cognition (e.g. benefits in memory and attention) and brain function (e.g. activation of working memory seen in functional MRI).” 
From the gathered studies, it could not be determined that single constituents of green tea is responsible for these nootropic effects.
Both caffeine and L-theanine together seem to influence cognition. The impact of these compounds was decreased when each was given in isolation. 
This herb may also exhibit neuroprotective effects due to its high concentration of antioxidant compounds.
Green tea extract continues to be studied in conditions like Parkinson’s disease, Alzheimer’s disease, dementia, depression, and for general cognitive function.
Green tea supplements are commonly used for aiding weight loss results. As a stimulant, it may boost energy levels, increase metabolism and help to suppress appetite.
The results from human trials are mixed, although benefits have been observed in some trials.
Preliminary clinical research show that green tea extract may increase fat and calorie metabolism due to the caffeine, catechins, and L-theanine content.
Resting energy expenditure and cellular thermogenesis (heat production) have been shown to increase following caffeine consumption. 
Studies using specific green tea extract products have demonstrated weight loss effects in overweight and obese patients.  Many of these products contain combinations of multiple fat-burning ingredients.
According to MNT, “Green tea may promote a small, non-significant weight loss in overweight and obese adults; however, since weight loss in the studies was so minimal, it is unlikely that green tea is clinically important for weight loss.” 
Green Tea Extract Supplements
According to Examine, there is little difference between the use of green tea in liquid form as a drink compared to taking oral capsules. The only differences will pertain to dosage and taste. 
The UMM states that most green tea extract supplements contain ground and powdered dried leaves in capsules. Liquid extracts, powders, and tablets are also available. Caffeine-free products are also available for those who do not want any stimulatory effects. 
Most green tea extract supplements provide between 400-1000 mg of extract, typically standardized to 40-50% EGCG content, although some are a lower standardization level.
The NMCD states that there are more than seven thousand different dietary supplements for sale that contain this herbal extract as a single ingredient or in combination with other ingredients.
When possible, look for organic, non-GMO, contaminant-free products produced by well-reputed manufacturers. Store green tea supplements in cool, dark, dry places in airtight, light-resistant containers to maintain their efficacy. 
Green Tea Extract Dosage
Most dosages used in research studies have been standardized according to EGCG content. Although it varies, the average amount of EGCG in one cup of C. sinensis green tea is 50 mg. 
The effects of green tea extract catechins are known to be dose-dependent, meaning that higher dosages of catechins induce stronger effects. 
In human studies, significant effects typically occur only at high doses. Products containing the equivalent of 400-500 mg EGCG daily have been studied. The majority of green tea supplements contain about 50% EGCG. 
Some green tea dosages that have been used in research studies include:
- Breast cancer: 3 sups or more tea per day
- Hyperlipidemia: 150-2500 mg catechins per day for up to 24 weeks
- Mental alertness: 720 mg two times per day for 16 weeks
- Obesity: 870 mg catechins two times per day for 8 weeks
- Prostate cancer: 200 mg catechins three times per day for one year
- Stress: 300 mg extract for 7 days 
It is recommended to discuss the best dose of green tea extract for your needs with your doctor.
Side Effects and Interactions
The Natural Medicines Comprehensive Database rates green tea as Likely Safe when consumed as a drink in moderate amounts. It is rated as Possibly Safe when used orally as a dietary supplement.
Green tea is rated as Possibly Unsafe when used orally in high doses long-term, and Likely Unsafe when used orally in very high dosages. Excessive consumption may be dangerous due to the caffeine content and adverse effects associated with this stimulant.
Green tea is generally very well tolerated either as a drink or as a supplement. Side effects are typically only reported at higher dosages and are generally mild gastrointestinal effects such as nausea, abdominal pain, and diarrhea. 
Be careful drinking green tea or taking extract supplements if you are sensitive to the effects of caffeine. Individuals with low caffeine tolerance could experience nausea, jitteriness, rapid heartbeat, and other related side effects. 
Do not use this supplement if you take prescription blood thinning medications. This tea contains vitamin K which is known to affect blood platelet aggregation. Using this supplement with blood thinners might increase the risk for bleeding and bruising. 
Green tea is not generally recommended for people with hypertension, liver or kidney problems, anxiety disorders, stomach ulcers, or heart disease. Use in pregnant or breastfeeding women is also not recommended due to the caffeine content. 
This herbal extract may interact with drugs or supplements including:
- Anticoagulant drugs, herbs, and supplements
- Caffeine-containing herbs and supplements
- Folic acid
- Monoamine oxidase inhibitors (MAOIs)
- Stimulant drugs
- Warfarin (Coumadin)
The NMCD reports more possible interactions with prescription drugs, over-the-counter medications, herbs, supplements, foods, laboratory tests, and diseases.
It is recommended to discuss possible interactions with your healthcare provider before using a green tea extract supplement.