Tea should be avoided during medication, and it should not be used to take medicine. Because substances in tea can react with various medications, reducing their efficacy. For example, tannins in tea can bind with iron supplements, calcium supplements, etc., to form precipitates that are not absorbed and thus become ineffective. Other substances such as enzyme preparations, antibiotics (like oxytetracycline), berberine, strychnine, quinine, ephedrine, rifampicin, codeine, as well as traditional Chinese medicine ingredients such as Corydalis, Cirsium japonicum, Cirsium setosum, and Aconitum, can also reduce or nullify the drug's effect by forming precipitates. Tetracycline and erythromycin can inhibit the metabolism of theophylline, increasing its toxicity; therefore, patients taking these medications should not drink tea.
Caffeine stimulates the central nervous system. Therefore, individuals with high blood pressure or insomnia should avoid tea. Because theophylline can raise body temperature, patients with a fever should not drink tea when taking aspirin. Tea should also not be consumed before or after meals.
Drinking tea before a meal dilutes saliva, making food tasteless afterward. Drinking tea after a meal affects the digestion and absorption of protein, vitamins, and minerals due to the action of tannins. People with chronic gastritis should also avoid drinking tea, as tannins in tea can irritate the gastric mucosa, causing discomfort.
Pregnant women should not drink tea.
Because tea contains tannins, which can affect the absorption of iron; additionally, the caffeine in tea is stimulating and can increase fetal movement, affecting the fetus's growth and development. Lactating women should also avoid tea. After being absorbed, the tannins in tea enter the bloodstream and have an astringent effect, inhibiting mammary gland secretion and causing a reduction in milk production. Moreover, the stimulant effect of caffeine not only affects the mother's rest but is also passed to the infant through breast milk, making the infant restless and affecting its health. Therefore, women during these special periods should temporarily overcome their tea-drinking habit for the sake of their own and their child's health.
Infants and young children should not be given tea. The tannins in tea can irritate the gastrointestinal mucosa, affect iron absorption, and lead to anemia. The stimulation of caffeine in tea can over-excite a child, preventing them from resting properly. Drinking tea can also accelerate a child's heart rate, damaging their cardiac and brain function, and increased urination can affect their kidney function.
Thus, while tea is beneficial, it is not something that everyone can enjoy at all times.