Drinking oolong tea can cause headaches, nervousness, sleep problems, vomiting and diarrhea, according to WebMD. It can also cause irritability and confusion. These side effects are due to the caffeine content of the tea.
Oolong tea is made from the leaves, stems and buds of the Camellia sinensis plant, notes WebMD. There are 50 to 60 milligrams of caffeine in each cup of oolong tea, and the suggested daily caffeine intake for adults is not to exceed 400 milligrams. Consuming an excess of caffeine can cause various side effects. If pregnant women drink more than 2 cups of oolong tea a day, the caffeine could induce premature delivery and low birth weight. Breastfeeding moms who drink oolong tea could cause their infants to be increasingly irritable or have overly frequent bowel movements.
Those with anxiety conditions who consume an excess of caffeine can experience an increase in symptoms. Caffeine can cause or worsen heart conditions, as some people experience irregular heart beats after consuming caffeine, according to WebMD. The caffeine in oolong tea increases the pressure behind the eye, which is known as glaucoma. This pressure occurs within 30 minutes of consuming the caffeine and lasts for at least 90 minutes.
There is some evidence that drinking approximately 6 cups of oolong tea a day for 30 days could help to lower blood sugar in those with type two diabetes, but, according to WebMD, studies have shown that drinking tea does not help to prevent the disease.