Green tea extract is an herbal product that is derived from processed green tea leaves. It contains antioxidants that have a number of therapeutic benefits. The Journal of Medicinal Studies says that green tea extract boosts alertness and enhances memory. Studies also show that green tea extract may have a positive effect on cognitive health. Yet, you will be surprised to know that it causes some side effects, making it a classic example for the saying - Even a medicine taken in excess becomes poison! Green tea leaves are steamed at high temperatures, which enables the extract to maintain important molecules called polyphenols that are said to be responsible for many benefits that it renders. But, its excess consumption might cause problems and side effects in people who have a sensitive system, or are on prescribed medication. • Psychological Problems: Some people tend to feel restless, confused and also irritated. A few of them may also suffer from sleeping disorders. • Skin Problems: A study conducted by Natural Standard found that the tannins and caffeine in green tea extract can cause allergic reaction. Excess consumption of green tea extract may result in itching and rashes. It is best to discontinue the consumption of the extract and seek medical advice. • Digestion Problems: A study conducted by the University of Maryland Medical Center shows that caffeine in green tea extract can increase the toxic levels in your system, if consumed heavily. In some cases, people might suffer from an upset stomach, nausea, vomiting, stomach ache, constipation and diarrhea. Some people might also suffer from frequent urination. Loss of appetite is also one of the common problems. • Calorie Block: Green tea has negligible calories and the substances in it promote weight loss through enhanced metabolism and appetite suppression. However, it can also block calories along with other nutrients, like vitamin B, which are vital for the functioning of our body. Hence, there are chances that a person may suffer from diseases which are caused due to the lack of these nutrients. Chances of the occurrence of such a condition, however, is very rare. • Other Problems: National Center for Complementary and Alternative Medicine has reported that green tea extract can harm the kidneys and liver. In some cases, it can also cause heart palpitations. Some people have also known to have suffered thyroid problems. • People suffering from anemia, diabetes, glaucoma, or osteoporosis should seek advice from their health-care provider before consuming green tea, or its extract. • Excess intake of caffeine through other beverages, and also green tea extract, for a long duration can cause irritability, insomnia, heart palpitations, and dizziness. An overdose can also cause nausea, vomiting, diarrhea, headaches, and loss of appetite. You may suffer from caffeine poisoning if this intake is so much that you start vomiting at some point, or have abdominal spasms. An immediate course of action is to limit the intake and rush to your doctor. • Pregnant and nursing women should especially avoid green tea and its extract as it contains catechins, caffeine and tannic acid. During early stage of pregnancy, green tea should be avoided completely. • Young children should also avoid consuming green tea extract as the caffeine present in it, however negligible, can lead to over stimulation. • People who are on previous medication should avoid green tea extract as it can cause an adverse interaction. In such cases it is best to consult a doctor before consumption. • Green tea extract can also interfere with the iron intake, hence it is advised not to drink it along with meals. There is no doubt that green tea extract possesses healing qualities. The antioxidant in it is especially useful in the fight against cancer, atherosclerosis, high cholesterol, liver diseases and many more ailments. However, its flip-side too, should be taken into account before enlisting its consumption in your daily habit. The dosage of green tea extract will vary according to the brand and quality of extract. So, read labels carefully and do not exceed the recommended quantity. Disclaimer: This Buzzle article is for informative purposes only, and should not be used as a replacement for expert medical advice.