Respected Contributor
Posts: 2,164
Registered: ‎03-10-2010
"A molecular docking study of EGCG and theaflavin digallate with the druggable targets of SARS-CoV-2": "Hypothesis: The role of tea polyphenols in prophylaxis and treatment of COVID-19 was established in this study."
"Antiviral activity of green tea and black tea polyphenols in prophylaxis and treatment of COVID-19: A review": "EGCG and theaflavins, especially theaflavin-3,3'-digallate (TF3) have shown a significant interaction with the receptors under consideration in this review. Some docking studies further emphasize on the activity of these polyphenols against COVID-19."
I thought these studies were interesting, and even important.  Perhaps regular tea drinkers who are not fans of coffee are less susceptible to developing COVID-19 symptoms?  I sure would love to know the answer to this.
Honored Contributor
Posts: 12,440
Registered: ‎11-24-2013

Re: Black and Green Tea

[ Edited ]

When I was having chemo in 2017 I drank a cup of green tea almost daily. It made me feel better but I have no idea why!


EDITED TO ADD: My oncologist was perfectly ok with this.

Respected Contributor
Posts: 4,775
Registered: ‎07-26-2019

Green Tee info from  webmed . Article also cautions interactions with medications  and those with heart diease.


" Green tea might slow blood clotting. Taking green tea along with medications that also slow clotting might increase the chances of bruising and bleeding.
Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others. "

Respected Contributor
Posts: 2,164
Registered: ‎03-10-2010

Anything can have a downside, @skatting44 , but if there are no contraindications to drinking tea, tea drinking should be just fine.


It is strange that Web Med indicates that green tea "might slow blood clotting", because  Green tea contains Vitamin K, which clots the blood, and, "Green tea is included in a list by Mayo Clinic's Sheldon Sheps, M.D., of foods to avoid while taking the blood thinning medication warfarin due to its high content of vitamin K, which has blood clotting effects that may counteract the blood thinning effects of warfarin. The average daily allowance of vitamin K for men is 120 mcg and for women 90 mcg. On the contrary, information provided by St. Luke's Family Practice indicates that brewed green tea contains negligible amounts of vitamin K. Consult your doctor to determine if green tea is appropriate for your health situation."  That quote comes from The Effects of Green Tea on Blood Clotting at Livestrong dot com 


Seems that the effects of green tea on warfarin, at least may depend upon the amount of tea consumed. 


Risks versus benefits should always be weighed, and medical professionals should be consulted when in doubt.  I guess the question is how much tea affects the medications in question, and the use of the word "might" in the first sentence of the quote you provided from WebMD makes me wonder why this has not been fully tested in medical research, if there is such concern about green tea.  Tea is one of the most popular drinks in the world.


Esteemed Contributor
Posts: 6,685
Registered: ‎05-15-2014

This is interesting.  I have a childhood friend of the family who is a pharmacist and told me to drink Matcha green tea for it's nutrients and antioxidants during my chemo therapy.

I had a nice soothing cup of it everyday.  

Esteemed Contributor
Posts: 5,892
Registered: ‎03-10-2010

There are probably a lot of other factors involved.

I know I had - something - last March. I had 1 day of aches, but nothing else. I am generally very healthy, on no meds, and do drink a lot of different teas. (Also take supplements & walk every day.)


If you have a healthy constitution, not just genetically, your immune system kicks in high gear when something is invading your health.


But thanks for the studies about tea! All the colors of tea seem to be very healthy. I try to drink 2-3 cups of green, but I can only hold so much liquid, ya know?

Honored Contributor
Posts: 16,140
Registered: ‎03-16-2010

@Harpa wrote:

There are probably a lot of other factors involved.

I know I had - something - last March. I had 1 day of aches, but nothing else. I am generally very healthy, on no meds, and do drink a lot of different teas. (Also take supplements & walk every day.)


If you have a healthy constitution, not just genetically, your immune system kicks in high gear when something is invading your health.


But thanks for the studies about tea! All the colors of tea seem to be very healthy. I try to drink 2-3 cups of green, but I can only hold so much liquid, ya know?



Tea affects me much more than coffee! 

Three cups and I'd never be able to leave the bathroom!😆

Honored Contributor
Posts: 8,736
Registered: ‎02-19-2014

Green tea contains more caffiene than coffee or espresso. So it's important to watch your intake.


From Sencha Tea Bar, a company that sells green and black tea:

1. Stomach Problems

Green tea may cause stomach irritation when brewed too strongly or consumed on an empty stomach (1). Green tea contains tannins that can increase the amount of acid in your stomach. Excess acid can lead to digestive issues including constipation, acid reflux, and nausea. Brewing green tea with water that is too hot can exacerbate these side effects. Brew your green tea with water between 160 and 180 F.


Green tea can also cause diarrhea when consumed in large amounts. Caffeine produces a laxative effect as it stimulates the colon muscles to contract and release more frequently. This results in more frequent trips to the bathroom and can cause upset stomach. If you suffer from irritable bowel syndrome, avoid green tea.


To avoid these side effects, do not drink green tea on an empty stomach. Instead, consume green tea after each meal. If you suffer from acid reflux disease, stomach ulcers, avoid green tea since it can increase acidity.

2. Headaches

Green tea can cause headaches in certain individuals since it contains caffeine (2). People who suffer from migraines can consume green tea occasionally. However, you should avoid drinking green tea every day if you suffer from daily headaches. If you have caffeine sensitivity, avoid drinking green tea.

3. Problems Sleeping

Green tea contains a compound that is antithetical to sleep: caffeine. Green tea contains only small amounts of caffeine, but may still cause problems sleeping for people sensitive to caffeine. This is due to the fact that chemical compounds in green tea prevent the release of hormones such as melatonin, which aid in sleep.


Green tea also contains l-theanine, a chemical that helps to induce calm, but also increases alertness and focus—something that may disrupt sleep for some individuals. Some research shows that l-theanine is beneficial for sleep; however, these studies have mainly been conducted on individuals with disorders including ADHD and schizophrenia (3)(4). Additional research shows that l-theanine may aid sleep by lowering heart rate through the inhibition of glutamate receptors in the brain (5).

These benefits may be outweighed by the presence of caffeine in green tea—particularly in matcha green tea. While research shows l-theanine is beneficial for sleep, there is no agreed upon dosage for it's effectiveness in the medical community. While most people may benefit from a cup of green tea before bed, people with caffeine sensitivity should consume it no later than 5 hours before bed.

4. Anemia and Iron Deficiency

Green tea contains antioxidants that hinder the iron absorption in the human body. A meta-analysis showed that this side effect can be a particularly dangerous for people who suffer from anemia or other disease where iron deficiency is present (6).


One case study found that green tea caused anemia in a 48 year old businessman who consumed 1500 milliliters (6 cups) of green tea every weekday for years (7). To avoid this side effect, add lemon to your tea. The vitamin C in lemon promotes iron absorption, counteracting this side effect. Alternatively, you can consume gren tea one hour before or after a meal. This gives your body time to absorb iron without the inhibition caused by tannins. As a precaution, avoid green tea if you have anemia.

5. Vomiting

Excessive amounts of green tea can lead to nausea and vomiting. That's because green tea contains tannins that have been linked to nausea and constipation because of the way proteins bind in the intestines (8). Avoid consuming more than 4 cups of green tea each day if you are a seasoned tea drinker. If you're just starting out with green tea, start with 1 or 2 cups per day and monitor your reaction. Only increase consumption if you experience no side effects.

6. Dizziness and Convulsions

The caffeine in green tea can cause you to feel dizzy or lightheaded when consumed in large amounts. Caffeine decreases blood flow to the brain and central nervous system, resulting in motion sickness. In rare cases, consumption of green tea can lead to convulsions or confusion (9). In some cases, green tea consumption can also increase tinnitus, known as ringing in the ears. If you suffer from tinnitus, avoid drinking green tea.


Always drink green tea in moderate amounts and avoid if you are sensitive to caffeine. Research shows that the maximum tolerated dose in humans is equivalent to 24 cups of the beverage (10). As mentioned, most of these side effects are rare and occur only when consumed in excessive amounts or in individuals senstiive togreen tea ingredients.

7. Bleeding Disorders

In rare cases, green tea can trigger bleeding disorders (11). Compounds in green tea decrease levels of fibrinogen, a protein that helps clot blood. Green tea also prevents the oxidation of fatty acids, which can lead to thinner blood consistency. If you suffer from a blood clotting disorder, avoid drinking green tea.

8. Liver Disease

Green tea supplements and high consumption of green tea can lead to liver damage and disease (12). Experts believe this is due to a build-up of caffeine that can stress the liver. To avoid this side effect, avoid consuming more than 4 to 5 cups of green tea every day.

9. Irregular Heartbeat and Blood Pressure

Some small studies show that green tea may cause irregular heartbeat. This side effect is rare and more research is needed to examine the exact compounds behind the heart rate increase. While research shows that drinking tea can help lower blood pressure, some studies have shown that green tea may still effect blood pressure in certain individuals.


One study found that green tea raised blood pressure due to the presence of caffeine (13). Another study found that drinking green tea may interfere with certain blood pressure medications including Corgard (14). If you suffer from heart disease, seek medical advice from your healthcare professional before consuming green tea.

10. Bone Health

Excess consumption of green tea increases the risk of bone disease such as osteoporosis in sensitive individuals. Compounds in green tea inhibit the absorption of calcium, resulting in a deterioration of bone health (15). Limit your intake to 2 to 3 cups of green tea if you are predisposed to bone disease. If you consume more than that, make sure to take a calcium supplement to support bone health.

11. Risks for Pregnancy and Child Use

Tannins, caffeine, and tea catechins have all been linked to increased risks during pregnancy. Experts say that green tea in small amounts — no more than 2 cups per day — is safe during pregnancy and breastfeeding. Caffeine is passed through breast milk to infants so monitor your intake in coordination with your physician. Drinking more than 2 cups per day can lead to miscarriage and birth defects in children. Make sure to keep your caffeine intake below 200 milligrams per day.

Is Green Tea Safe?

While there are several side effects to watch out for, green tea is considered safe by the FDA when used in moderation. Most of these negative side effects are due to the caffeine content and only occur when the beverage is consumed in large amounts. Stick to suggested amounts and avoid green tea if you are sensitive to caffeine. If you suffer from any illnesses that predispose you to side effects, consult with your physician before drinking green tea.


When you’re accustomed to privilege, equality feels like oppression.
"Power without love is reckless and abusive, and love without power is sentimental and anemic." - Dr. Martin Luther King Jr
Respected Contributor
Posts: 2,164
Registered: ‎03-10-2010

@Porcelain - Drinking too much of anything can be dangerous-- even water.  


I will happily continue to enjoying drinking my tea.  


I am thrilled to read the good news in published medical research that drinking tea might actually help me avoid infection with SARS-CoV-2 and possibly lessen the severity of COVID-19 illness symptoms, too.  It is truly great news!

Honored Contributor
Posts: 32,439
Registered: ‎05-22-2016

Re: Black and Green Tea

[ Edited ]

I've been drinking pure (green tea) matcha since I can remember. I grew up drinking that kind of green tea. It's good for me. I take about 10 grams of the pure matcha powder everyday mixed in with my green drink.


This is the one I take. It's 100% pure Japanese matcha: