1. Insomniacs should avoid drinking tea at night: The stimulating effect of tea may make insomnia worse.

2. Avoid storing tea with strong odors: The high-molecular compounds in tea are chemically active. When tea comes into contact with soap, camphor, cigarettes, etc., it quickly absorbs their odors, giving the tea an unpleasant smell. Therefore, tea should be kept away from odorous substances, and storage containers must be clean and odor-free.

3. Do not drink tea before meals: Drinking tea before a meal dilutes saliva, making food taste bland. It also temporarily reduces the digestive organs' ability to absorb protein, affecting normal physiological functions and potentially leading to malnutrition over time.

4. Avoid drinking tea immediately after meals: After food enters the stomach, it requires various enzymes and gastric acid—which contains 0.5% hydrochloric acid—to be converted into absorbable nutrients. If tea is drunk right after a meal, its alkaline substances neutralize gastric acid, and the water dilutes digestive juices, prolonging digestion and increasing the stomach's burden. Over time, this can damage the stomach and harm health.

5. Do not chew tea leaves: Currently, air and soil are heavily polluted by fertilizers and pesticides, leading to excessive residues or heavy metals in tea. These substances do not easily leach into the tea infusion, but if tea leaves are chewed, they may accumulate in the body, posing health risks. Therefore, after drinking tea, the leaves should be discarded—no matter how good the tea is, remember not to chew the leaves.

6. Avoid taking medication with tea: Tannic acid in tea can precipitate with ferrous ions from iron supplements like ferrous sulfate or ferric citrate, hindering iron absorption and causing abdominal pain or constipation. Drugs containing alkaloids may also precipitate with tannic acid, reducing their effectiveness. Sedatives and antihistamines can be counteracted by caffeine in tea, lowering their efficacy. Sodium bisulfate-containing drugs may decompose when reacting with tannic acid, diminishing their effect. Tea's impact on drug efficacy depends on the amount and concentration consumed.

7. Avoid drinking tea when having a fever: Many people habitually drink hot, strong tea when catching a cold, often saying, "A cup of hot tea will make you feel better." However, this is not conducive to recovery. British pharmacologists have proven that theophylline in tea can raise body temperature and significantly reduce the effectiveness of fever-reducing medications. Therefore, do not drink strong tea when feverish.

8. Anemic patients should avoid tea: Anemia, especially iron-deficiency anemia, is common. Iron deficiency impairs hemoglobin synthesis, leading to pale complexion, dizziness, fatigue, and shortness of breath. Drinking tea can worsen anemia because tannic acid in tea readily binds with ferrous iron, forming insoluble tannin-iron compounds that block iron absorption. Thus, anemic patients should avoid tea.

9. Young women should avoid strong tea: During adolescence, menstruation has just begun, and the body is still adapting. Menstrual blood contains high levels of hemoglobin, plasma proteins, and heme. Strong tea contains high amounts of tannic acid, which combines with iron in food to form tannin-iron salts, hindering iron absorption in the intestinal mucosa and potentially causing iron-deficiency anemia. Additionally, the high caffeine content in strong tea accelerates heartbeat and increases urination, placing extra strain on the heart and kidneys. Therefore, young women should avoid strong tea.

10. Do not drink excessive amounts of tea: Tea contains the trace element fluoride. Although fluoride is an essential trace element, the daily physiological requirement is only 1–1.5 milligrams. However, fluoride levels in tea are 10 to hundreds of times higher than in other foods. Consuming fluoride beyond safe limits can lead to chronic toxicity. Fluoride poisoning manifests as tooth discoloration (yellow, brown, or black) and skeletal fluorosis (pain in limbs and spine, joint deformation, paralysis). Hence, tea should not be consumed in excess.

11. Avoid drinking strong tea on an empty stomach in the morning: Drinking strong tea on an empty stomach can overstimulate kidney function, causing frequent urination and palpitations. It also impairs gastrointestinal function and hinders the absorption of iron and vitamin B1.