Although drinking tea has many benefits, excessive consumption or drinking tea at unsuitable times can sometimes lead to side effects. For example, it is appropriate for patients with neurasthenia to avoid drinking tea at night to prevent insomnia. Those with neurasthenia often feel lethargic and lack energy during the day but have trouble sleeping at night. These individuals may try to regulate themselves with tea. They can drink a cup of mild tea after breakfast and another cup of light tea (premium green tea is recommended) in the morning. However, it is not advisable to drink tea after dinner to avoid overstimulation.

People with spleen-stomach deficiency and cold, or those suffering from gastric and duodenal ulcers, should not drink strong tea. It is especially important to avoid drinking tea on an empty stomach to prevent aggravating stomach discomfort. Such patients can drink some mild tea half an hour after meals.

Generally, it is not advisable to drink strong tea on an empty stomach, as it can inhibit gastric acid secretion, hinder digestion, and even cause symptoms such as palpitations, headaches, stomach discomfort, dizziness, and irritability. This is known as "tea intoxication." If this occurs, sucking on candy or drinking some sugar water can alleviate the symptoms. Pregnant women, in particular, should avoid strong tea. When pregnant women drink strong tea, the caffeine in the tea leaves is absorbed not only by the mother but also by the fetus. Studies show that the metabolism of caffeine in the fetus is much slower than in adults, meaning its effects last longer, which is unsuitable for fetal growth and development. To avoid excessive stimulation of the fetus by caffeine, it is better for pregnant women to drink less tea.