Because tea contains theophylline, theophylline is a substance that can excite the central nervous system, which can make a person’s spirit hyperactive, increased nervous excitability, and difficult to fall asleep. Especially people who are more sensitive to substances, after drinking strong tea will often insomnia, so should try to avoid drinking strong tea at night. In addition, strong tea can also cause an increase in blood pressure, increased heart rate, so patients with high blood pressure, heart disease should try not to drink strong tea. Strong tea also has damage to the gastrointestinal tract, can dilute stomach acid, causing symptoms of indigestion, often drink strong tea can easily lead to bloating, flatulence and other discomfort. Normally, a cup of water with about 3g of tea is enough, and a cup of tea can be brewed three times.