Green tea is a beverage made from extracts from the Camellia sinensis plant.
Green tea is often used to increase mental awareness, prevent dizziness upon standing and reducing the risk of bladder, esophageal, pancreatic and ovarian cancer. However, as with most supplements, there are negative effects associated with imbibing green tea.
In rare cases, you may develop a severe allergic reaction to green tea. Difficulty breathing, tightness or closing of your throat, hives and swelling of the face and tongue are all possible symptoms of an allergic response, Drugs.com warns. If you experience any of these effects right after taking green tea, seek immediate medical attention. Severe allergic responses can lead to respiratory arrest and death. Once you know you are allergic to green tea, avoid it and any other foods or beverages that contain it.
Green tea can negatively affect your digestive system, according to MedlinePlus, a service of the National Institutes of Health. Some people taking green tea will develop stomach pain, heartburn and constipation. Conversely, some patients will experience severe diarrhea once they take large amounts of green tea. Furthermore, green tea decreases the rate your gastrointestinal can absorb iron. This decrease in iron absorption may lead to iron-deficiency anemia.
Large doses of green tea, usually more than 5 cups a day, may cause changes in behavior and other psychological effects. You may experience an increased sense of nervousness and anxiety, Drugs.com reports. Some patients will become more irritable and possible violent. You may also notice that you are having problems in sleeping. These negative effects disappear as the dosage of green tea is decreased.
One of the more severe side effects of green tea is a caffeine overdose. Excessive and long-term intake of green tea increases the amount of caffeine within the body . The initial symptoms of caffeine overdose include a severe headache, abnormal heartbeat, tremors, dizziness, convulsions, confusion and a ringing sensation in the ears, MedlinePlus notes. Dosages greater than 10 g to 14 g per kg can kill you. If you think you have overdosed on green tea, seek emergency medical attention.
While high fluid intake is commonly recommended in people who have a history of kidney stones, tea has been found to increase the oxalate levels in the urine. Calcium oxalate stones are one of the more common types of kidney stones. There are concerns among some health care professionals that drinking tea can increase the risk of stone development.
Green tea can interact with a number of medications or supplements. Among the most important of these, green tea may inhibit the action of adenosine, a heart medication; reduce the sedative effects of benzodiazepines; increase blood pressure in people who take propanolol and metoprolol, and reduce the effects of lithium and clozapine, which are taken for mental illness. Green tea may cause a severe increase in blood pressure in people who take monoamine oxidase inhibitors, which are used to treat depression. Green tea in high amounts can interfere with the anticoagulant Coumadin, making it less effective. According to the Linus Pauling Institute, tea can also interfere with the absorption of iron from plant substances and supplements; a cup of tea can decrease the amount of iron absorbed by about 70 percent.
When it comes to cancer, green tea has pluses and minuses. Although green tea shows some promise in various studies on cancer prevention, the University of Maryland notes that at least one large study indicated it may increase the risk of esophageal cancer, and that the stronger and hotter the tea, the higher the risk. Green tea also has mixed results in chemotherapy. The combination of green tea with doxorubicin and tamoxifen showed the drugs were more effective in laboratory tests. But green tea extract can stimulate a gene in prostate cancer cells that may decrease sensitivity to chemotherapy drugs, and the University of Maryland recommends that men receiving chemotherapy for prostate cancer should not drink green tea.