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Tea plant
CautionTeestrauch · (Camellia sinensis)
Tea family (Theaceae)
Description
The tea plant is an evergreen shrub or small tree of the tea family, originally from the border region between south-west China, north-east India and Myanmar. Left alone it would grow several metres tall; on plantations pruning keeps it at waist height so the young shoots can be picked by hand. Usually only the bud and the two following leaves are taken. Its leathery, serrated leaves are the source of every true tea — green, white, oolong and black. The differences come not from different plants but purely from processing: green tea is heated right after picking so the leaf enzymes are killed off; black tea is allowed to oxidise first, which gives it its colour and malty note; oolong sits in between. The leaves contain caffeine, the amino acid L-theanine and polyphenols — chiefly the catechins, including the much-studied EGCG. As a beverage, tea is considered safe for adults. Concentrated green tea extracts are a different matter — see the safety section for details.
Critical drug interactions with:
Leberbelastende Arzneimittel und Grüntee-Extrakte
Tea contains caffeine and has a stimulating effect; it is traditionally consumed as a beverage for enjoyment and alertness. The L-theanine in the leaf softens the caffeine effect somewhat — which is why it is often felt as calmer than coffee. How much caffeine ends up in the cup depends strongly on steeping time and water temperature.
Preparation & dosage
Green tea does not take boiling water: 70–80 °C, one to three minutes. Too hot or too long and the tannins turn it bitter. Black tea, by contrast, with boiling water, three to five minutes.
- Doses per day
- 4×
The leaves are rich in catechins (especially EGCG) with antioxidant properties in the lab. Studies suggest a modest reduction in cholesterol; a proven health benefit in humans is not established. The US NCCIH sums up the position as there being no established benefit of green tea for any disease — what convinces in the lab has so far not kept pace in humans.
The polyphenols in tea bind plant iron in the gut and considerably reduce its absorption — an effect well measured in humans. For most people this is irrelevant; with iron deficiency, in pregnancy or on a vegetarian diet it is worth drinking tea one to two hours away from meals. Vitamin C with the meal works in the opposite direction.
Sources: [4]
Tea as a beverage is considered safe for adults. Its caffeine can affect sleep, heart rate and blood pressure; limit caffeine during pregnancy and breastfeeding. Tea with meals markedly inhibits absorption of plant iron — if iron-deficient, drink it away from iron-rich meals. Concentrated green tea extracts (capsules) have been linked to rare but serious liver injury; the EU limits EGCG to under 800 mg per day. Green tea may alter the effect of some medicines.
Customary as a beverage in moderation, but the caffeine counts towards the daily total. Tea also inhibits iron absorption, which is unhelpful in pregnancy — keep a gap from meals. Green tea extracts in capsule form are not appropriate.
Caffeine passes into breast milk, and infants break it down far more slowly than adults. A few cups spread over the day are considered acceptable; larger amounts can make the baby restless.
Because of the caffeine and the inhibited iron absorption, not suitable as an everyday drink for small children. Green tea extracts do not belong in children's hands at all.
Drug interactions
Eisenpräparate
The polyphenols bind iron in the gut and markedly reduce absorption. Take iron tablets and tea at least one to two hours apart.
Gerinnungshemmer vom Cumarin-Typ (Warfarin, Phenprocoumon)
Green tea contains vitamin K, which can weaken the effect of these agents. The occasional cup is not the problem — a sudden change in the daily amount is.
Leberbelastende Arzneimittel und Grüntee-Extrakte
Liver injury is documented for high-dose extracts. Together with liver-burdening medicines or alcohol, such supplements are inadvisable.
Koffeinhaltige Mittel und Stimulanzien
The caffeine from tea adds to other sources — palpitations, restlessness and sleep problems can follow.
Contraindications
- High-dose green tea extracts with existing liver disease. The liver injury is idiosyncratic — it depends less on the amount than on individual predisposition, usually appears within one to six months and runs like an acute hepatitis. In one case series 35 % of cases were severe and 8 % required a liver transplant. Drinking tea itself is not affected by this.
- Marked iron deficiency — in that case drink tea only well away from meals.
Harvested part: Leaves
- Time of day:
- The bud with the two following leaves is picked, in the early morning. The first flush in spring is considered the finest; after that the shrub pushes out new growth every one to two weeks.
- Drying:
- For green tea, heat the leaves within a few hours — stirred in a wok or briefly steamed — to kill the enzymes; then roll and dry. If instead they are left to wither and rolled only afterwards, they oxidise and black tea results.
- Storage:
- 12 months — Airtight, dark, cool and far away from spices — tea takes on foreign smells. Green tea fades faster than black.
- KoffeinAlkaloidContent: 2–4 %Leaf
Highest in the bud, lower in older leaves.
- Catechine (EGCG, EGC, ECG)FlavonoidLeaf
Preserved in green tea; in black tea largely converted to theaflavins by oxidation. EGCG is also the compound that can burden the liver in extracts.
- L-TheaninOtherLeaf
An amino acid responsible for the umami-like taste that softens the caffeine effect.
- Theaflavine und ThearubigineTanninLeaf
Formed only during oxidation — they make black tea dark and mellow.
- Tannine (Gerbstoffe)TanninLeaf
- FluoridMineralLeaf
- Vitamin KVitaminLeaf
- [1]MonographA Comprehensive Insight on the Health Benefits and Phytoconstituents of Camellia sinensis (Antioxidants 2019, PMC6826564)(accessed: 2026-06-23)
- [2]MonographGreen Tea — NCCIH (NIH)(accessed: 2026-06-23)
- [3]MonographGreen Tea — LiverTox (NIH, NBK547925)(accessed: 2026-08-20)
- [4]MonographInhibition of non-haem iron absorption in man by polyphenolic-containing beverages (British Journal of Nutrition)(accessed: 2026-06-23)
- [5]CommonsFile:Csinensis.jpg — Wikimedia Commons(accessed: 2026-06-23)