Black tea is a product made from the Camellia sinesis plant. The aged leaves and stems are used to make medicine. Green tea, which is made from fresh leaves of the same plant, has some different properties. Black tea is used for improving mental alertness as well as learning, memory and information processing skills. It is also used for treating headache and low blood pressure; preventing heart disease, including “hardening of the arteries” (atherosclerosis) and heart attack; preventing Parkinson's disease; and reducing the risk of stomach and colon cancer, lung cancer, ovarian cancer, and breast cancer. It is also used for type 2 diabetes, stomach disorders, vomiting, diarrhea, and as a diuretic to increase urine flow. Some people use black tea for preventing tooth decay and kidney stones. In combination with various other products, black tea is used for weight loss. In foods, black tea is consumed as a hot or cold beverage. How does it work? Black tea contains 2% to 4% caffeine, which affects thinking and alertness, increases urine output, and may reduce the symptoms of Parkinson's disease. It also contains antioxidants and other substances that might help protect the heart and blood vessels.