According to Abdopain.com, drinking too much tea can cause constipation. Drinking a lot of tea causes the body to lose more water via the urine. The body then tries to compensate the loss by drawing water from the feces, thus making it hard and difficult to pass.
According to a study published in PubMedCentral, a group of healthy volunteers drank water for one week and tea the next week. After the tea consumption, they were noted to have decreased bowel movement transit time.
Tea is believed to cause constipation due to its theophylline, tannin and caffeine, which act as diuretics. According to the Mayo Clinic, diuretics remove salt and water from the body via urine. This lessens available water in the stool as well and makes it hard to pass.