Camelia sinensis L.


It is a very branched sapling that in the wild can reach 4 to 10 m in height, but in cultivation it is not allowed to exceed 1 m in order to keep the foliage dense and to be able to harvest the leaves easily. The leaves can have different dimensions, depending on the variety and origin. They are persistent, simple, with short petiole, oval-oblong, acuminate and with finely serrated edges in the basal 2/3. The young leaves are soft and tomentose, later they become leathery and glabrous. The flowers are creamy-white, axillary, solitary in groups of 2 to 3 in the axils of the leaves. The fruit appears in a rounded capsule that encloses the seeds. The 2 most known varieties of tea are Camellia sinensis and C. Assamica. They belong to the Theaceae family.


The use and cultivation of tea in the Orient is so ancient that it is not known for sure which is the native land of the shrub. It is assumed to be native to India, where it grows wild in the basin of the Brahmaoutra River, a tributary of the Ganges. It is now cultivated in many tropical and subtropical regions, especially in China, India, Japan, Sri Lanka, Indonesia and Brazil.

Composition and properties

Part used


In the case of green tea, the leaves are harvested and stabilized by steam (under pressure) to inactivate the oxidative enzymes; the leaves are then dried during a short period of rapid heating to preserve the bioflavonoid content (it does not undergo any fermentation process). It consists of greenish-yellow to brownish-green leaf fragments, whose original structure is visible to the naked eye.

Active principles

There are multiple factors that influence the composition of tea, which varies like other plants, according to climate, season, cultivation practices, variety, age of the leaves (the older the leaves are, the lower the quality decreases), etc.

However, the most important active principles are:

Polyphenolic derivatives among which stand out:

  • Flavonoids (5-10%): kampferol, quercetol, myricetol, etc.
  • Mostly catechin tannins: catechin, epicatechin, epicatechin gallate, gallocatechin, epigallocatechin, epigallocatechin gallate. These vary between 10-20% depending on the cultivar and age of the leaves. Catechins are colorless, astringent, water-soluble compounds. They are easily oxidized, although their degree of oxidation is variable. This property has been used to use them as an antioxidant in food. In the process of black tea formation, the catechin tannins are mainly oxidized and converted into pigments such as theaflavin, thearubigin, benzotropolone, theaflagalin.
  • Proanthocyanidols or condensed tannins: procyanidols, prodelphinidol, teasinensins, asamicains. Tea peroxidase may be involved in their generation.
  • Phenolic acids: malic, succinic, oxalic, chlorogenic, gallic, caffeic, coumarilquinic and one that only occurs in tea, treogalin (3-galloyl-quinic acid).

The xanthic bases or alkaloids: theophylline, theobromine and caffeine (also called theine). Some appear partially combined with tannins. Caffeine is present in an average of 3% along with very small amounts of other common methylxanthines, theobromine and theophylline.

It contains mineral salts (its fluorine content stands out, especially in the old leaves. We must keep in mind that tea also accumulates aluminum and manganese), vitamin C and B, substances that give color and aroma to the plant and that can appear in free form or combined in the form of glycosylates including traces of essential oil (aliphatic alcohols, methyl salicylate) and carotenoids (violaxanthin, beta-carotene, neoxanthin, lutein), amino acids (traces of adenine, xanthine and theamine (5-N-ethyl-glutamine); the latter is specific to tea and is often used to establish the quality of the plant), triterpene saponins and enzymes.

The composition of green tea is similar to that of the dried leaf, except for a few enzymatically catalyzed changes, which occur extremely rapidly after harvesting. New volatile substances are produced during the drying process. Oolong tea is halfway in its composition between green and black tea.

Pharmacological action

  • Stimulant of the central nervous system (xanthine bases). It seems that the mechanism of action of these alkaloids is related to the inhibition of cAMP phosphodiesterases, and to a lesser extent, of cGMP, thus increasing the concentrations of these cellular mediators. The stimulant action of green tea is milder but longer lasting than that of coffee. The effect of xanthan bases (especially caffeine and theophylline), which inhibit phosphodiesterase (thus favoring the activity of catecholamines by increasing cAMP) is modulated by polyphenols which, by blocking the enzyme O-methyltransferase, responsible for the destruction of adrenaline, keep it elevated in the blood for a longer time, with an added lipolytic effect.
  • It increases wakefulness and the capacity for physical exertion.
  • It produces cardiac stimulation (positive inotropic) and peripheral vasodilatation. It increases the heart rate favoring circulation and increasing blood supply, especially to the coronary arteries that irrigate the heart muscle, and to the rest of the body, including the kidney with a diuretic effect.
  • Stimulant of the respiratory center. Theine accelerates the transport of certain analgesics (aspirin, phenacetin) through the blood, and being a cardiorespiratory stimulant, it counteracts the depressive effect of alcohol, barbiturate and morphine abuse. The polyphenols make the action of theine less brutal but more pronounced than that of caffeine.
  • It stimulates brain activity, thus facilitating intellectual work.
  • Stimulates skeletal muscles.
  • Diuretic (xanthan bases and polyphenols). This action is due to the increase of glomerular filtration and decrease of tubular reabsorption.
  • Hypolipidemic or lipolytic (polyphenols). Green tea extract has been shown in laboratory animals to normalize the levels of total cholesterol, lipid peroxides and serum phospholipids. It prevents lecithin depletion without modifying triglyceride and HDL-cholesterol levels. It also produced a decrease in lipid accumulation in the liver and aorta. Epidemiological trials have shown a lower incidence of arteriosclerotic cardiovascular accidents in tea-consuming populations.
  • Antiplatelet agent (polyphenols).
  • Vasoprotective, venous tonic and vitamin P action (polyphenols: flavonoids and catechols). Produces vasoconstriction in the cerebral vascular bed.
  • Antioxidant, anti-inflammatory and immunomodulatory (polyphenols). Flavan-3-ols are inhibitors of lipid peroxidation at the mitochondrial level, acting as antiradicals. Catechins and other bioflavonoids exhibited antioxidant action similar to vitamin C and vitamin E, which have also been shown to reduce the risk of certain types of cancer when taken as supplements or in large proportions naturally in the diet. There is growing interest in the biological effects of tea-derived polyphenols and many in vitro and in vivo studies are demonstrating their antioxidant properties.
  • Bronchodilator. Xanthan bases produce relaxation of bronchial smooth muscle.
  • According to some authors it increases gastric acid secretion and according to others it protects the stomach against acidity and ulcers. Studies conducted in Japan with green tea (especially decaffeinated) served to observe its anti-ulcer effect since, in addition to its antibacterial action, it has the ability to stimulate the proliferation of cells and mucus of the gastric mucosa forming a protective barrier against hydrochloric acid.
  • Antitumor action. Different catechins and tea extracts have been tested in several animal models and in vitro, in tumor cells and established cell lines. They have shown inhibition of different biochemical processes related to carcinogenesis, especially cell proliferation, induction of apoptosis of neoplastic and paraneoplastic cells, as well as inhibition of tumor invasion and angiogenesis.
  • Protective action against dental caries. Due to its antibacterial action and its richness in fluorine, it can be used, in the form of rinses, to prevent the formation of dental plaque and prevent tooth decay. Its extract can be used as a breath purifier.
  • It decreases the absorption of certain nutrients. Tannins interfere at intestinal level with digestive enzymes. It has an inhibitory effect of the enzyme alpha-amylase, salivary and intestinal, so it has been used to control obesity and diabetes. In addition, it favors the "burning" of fat for energy by decreasing the availability of glucose.
  • Astringent. Black tea is less astringent than green tea, so it is very useful in case of diarrhea.
  • Antibacterial. Experimentally, its bactericidal action against the cholera vibrio has been proven, inhibiting its hemolytic activity, suggesting its usefulness as a cholera preventive. It has also been observed to have an antibacterial action, and in vitro studies have shown that catechins, especially in black tea, inactivate and inhibit influenza viruses.
  • Green tea has found an application in the field of complementary medical examinations, as it has been observed that it increases the clarity of magnetic resonance images of the digestive tract, making the head of the pancreas, the gastric walls and the descending portion of the duodenum more visible.
  • Theine accelerates the transport of certain analgesics (aspirin, phenacetin) through the blood, and being a cardiorespiratory stimulant, it counteracts the depressive effect of alcohol, barbiturate and morphine abuse. Polyphenols make the action of theine less brutal but more pronounced than that of caffeine. Theophylline is a smooth muscle relaxant, especially bronchial, diuretic and peripheral vasodilator. Theobromine is a diuretic and cardiac muscle stimulant.
  • Theanine is an amino acid commonly found in tea, capable of producing a feeling of relaxation. Theanine produces these effects by increasing the level of gamma-aminobutyric acid (GABA) production, affects the levels of serotonin and dopamine in the brain and inhibits the excitatory toxicity of glutamic acid. It is able to cross the blood-brain barrier. It is theorized that the association characteristics of theanine with GABA, reduce the stimulant power of caffeine contained in black tea, compared to coffee. It also promotes the production of alpha waves in the brain, commonly associated with wakefulness. Theanine is not eliminated in the decaffeination process, since it is not an alkaloid. Other research has found that L-theanine may aid in the body's immune response by enhancing the immune capacity of T-cells. However, these actions are minimal since the amount of theanine contained in tea is very small.


  • Asthenia, physical and intellectual exhaustion.
  • Hypotension (according to some authors it is hypotensive).
  • Diarrhea.
  • Coadjuvant in the treatment of obesity
  • Hypercholesterolemia.
  • Prevention of thromboembolism.
  • Edemas, oliguria, fluid retention.
  • In case of stomach ulcers, decaffeinated green tea should be used.
  • Dental caries.

Preparation methods

When hot water is poured over green tea, the soluble substances of the tea (caffeine, polyphenols and various volatile components such as essential oils) pass into the water at a rate of concentration that decreases with time.

To extract the full flavor of the tea, the water temperature for green tea should be between 70 and 95°C.

The two most outstanding actions of green tea are: its stimulating effect and its astringent effect. Depending on whether we want to use one or the other, we will prepare it.

  • If you want its stimulating effect: bring to boil, about half a glass of water, when it boils add 1 teaspoon of dessert of plant, boil 2 minutes and strain it. Cool and drink several cups a day.
  • If you want its astringent effect: bring to a boil, about half a glass of water, when boiling add 1 teaspoon of plant dessert, boil 10 minutes and strain. Cool and drink 2-3 cups a day. 

This is because caffeine is extracted quickly in hot water. However, if the boiling time is longer, the active principles that are extracted are the tannins, which bind to the caffeine and inactivate it, diminishing its stimulating effect.


  • People with known allergy or hypersensitivity to caffeine or tannins should avoid drinking tea.
  • Anxiety, nervousness and insomnia: due to its stimulating effect on the central nervous system.
  • Peptic ulcer and gastritis: due to the ulcerogenic effect of tannins and the stimulation of gastric secretion. According to some authors it protects the stomach against acidity and ulcers.
  • It is not recommended during the first trimester of pregnancy. Green tea in small amounts is considered possibly safe. However, it is not advised to drink more than 2 cups per day of green tea. This amount of tea provides about 200 mg of caffeine. Caffeine crosses the placenta and consuming more has been associated with miscarriages, intrauterine growth retardation, and low birth weight. Also, heavy caffeine consumption during pregnancy may increase the risk of later development of SIDS (sudden infant death syndrome). Caffeine in very high doses has been associated with genetic defects, including malformations of limbs or palate.
  • It is not recommended in breastfeeding. Xanthan bases can pass into breast milk and produce insomnia in infants.
  • In children under 12 years of age due to its stimulant effect.


  • Cardiac arrhythmia and arterial hypertension: due to the stimulating effect of the cardiovascular center of the medulla oblongata.
  • Hyperthyroidism: may aggravate hyperthyroid symptoms.
  • Spasmophilia.
  • Abundant fluid intake is recommended to avoid dehydration.
  • Caffeine in diabetics can produce unpredictable effects on blood glucose, either increasing or reducing blood glucose levels. Therefore, a moderate consumption of this substance in diabetics is recommended.
  • It has been observed that there is a significant correlation between a greater increase in the consumption of certain types of tea rich in condensed tannins (old leaves) and a greater tendency to develop esophageal cancer.
  • The potential benefits of moderate tea consumption (as it contains caffeine) are reinforced by drinking it with iron-poor foods.
  • Preliminary research has associated green tea with reduced estrogen levels in the body. However, it is unclear whether significant side effects may occur as a result.

Drug interactions

  • Caffeine interacts with monoamine oxidase inhibitors (MAOIs) potentiating their sympathomimetic effects that can result in cardiac arrhythmias or severe hypertension. Coffee consumption is contraindicated during treatment with MAOIs (e.g. furazolidone, procarbazine, and selegiline).
  • Caffeine can counteract drowsiness and mental slowness caused by benzodiazepines such as lorazepam (Ativan®) or diazepam (Valium®).
  • Barbiturates should not be administered together with caffeine either, firstly because they are the first inducers of hepatic metabolism with the consequent reduction of caffeine plasma levels and secondly because caffeine can cancel out the hypnotic effects of barbiturates. Other inducers of hepatic metabolism (phenytoin, rifampicin, etc) can also reduce the efficacy of caffeine.
  • May increase the effect of some coronary vasodilators (dipyridamole).
  • It may have a synergistic effect with sulindac and tamoxifen, reducing their undesirable effects.
  • Caffeine inhibits the antipsychotic effect of clozapine due to possible dopaminergic antagonism.
  • Caffeine can potentiate the stimulant effects of nicotine, beta-adrenergic agonists such as albuterol (Ventolin®) or other methylxanthines such as theophylline.
  • Caffeine can block the effects of adenosine, but this is only when plasma levels are very high, higher than those obtained using therapeutic doses. However, this antagonistic effect should be taken into account if high doses of caffeine are administered.
  • Caffeine should be avoided or used with caution if the patient is medicated with methylphenidate, modafinil, pemoline, pseudoephedrine or beta-blockers or other sympathomimetics. The combination of caffeine with these drugs can produce nervousness, irritability, insomnia and cardiac arrhythmias.
  • It can interact with warfarin.
  • Caffeine interferes with the effects of creatine (a substance used to increase the ergogenic effects of bodybuilding). A dose of 5 mg/kg/day of caffeine has been shown to completely eliminate the effects of creatine on muscle contraction, although caffeine does not interfere with the ability of creatine to increase the effects of phosphocreatine in muscle.
  • Xanthines: tea can potentiate the hyperexcitability produced by coffee, theophylline, mate, guarana, etc.
  • Digitalis: due to the hypokalemia it may produce.
  • Stimulant medications such as Ritalin: They could increase the stimulant effects of black tea.
  • When taken with caffeine, numerous drugs can increase caffeine levels in the blood or the time it acts in the body, some of these examples are disulfiram (Antabuse®), oral contraceptives or hormone replacement therapy, fluvoxamine (Luvox®), cimetidine (Tagamet®), verapamil and mexiletine.
  • Caffeine levels can be reduced with the ingestion of dexamethasone (Decadron®).
  • It is not recommended to use phenylpropanolamine and caffeine together because they can occasionally produce strokes, so co-administration of both drugs should be avoided.
  • Antibacterial quinolones (norfloxacin, ciprofloxacin, enoxacin, etc) reduce the elimination of caffeine, which may cause an exaggerated increase in the pharmacological effects of this substance.
  • Caffeine tends to increase lithium excretion.
  • Although caffeine alone does not appear to have pain-relieving properties, it is used in combination with ergotamine tartrate in the treatment of migraine or cluster headaches (Cafergot®). It has been shown to increase the headache-relieving effects of other pain relievers such as acetaminophen and aspirin (e.g. Excedrin®). Caffeine may also increase the palliative effects of codeine or ibuprofen (Advil®, Motrin®).
  • Due to their tannin content, if administered together, they can decrease the intestinal absorption of dietary iron and theophylline.

Side effects and toxicity

Tea generally does not produce adverse effects. The most frequent adverse effects occur in people who consume large amounts of tea per day. The side effects of caffeine (theine) are generally mild and transient; although individual differences may be important.os de la cafeína (teína) son generalmente leves y transitorios; aunque las diferencias individuales pueden ser importantes.

  • Digestive: gastralgia, nausea, vomiting, diarrhea or constipation, peptic ulcer, anorexia, due to its tannin content.
  • Neurological-psychological: insomnia, excitability, nervousness, and more rarely, tremors, palpitations, headaches.
  • Cardiocirculatory alterations: tachycardia, palpitations, hypertension, etc.
  • Renal: caffeine acts on the kidneys as a diuretic (increasing urine and urine sodium/potassium levels and potentially decreasing blood sodium/potassium levels), and may worsen incontinence.
  • Metabolic: elevation in blood sugar levels, iron deficiency, etc.
  • Hepatic. Hepatotoxicity of an extractive fraction of the plant has been described, and it has been withdrawn from the market in our country (Dueñas Sadornil C et al. 2004).

Chronic ingestion of caffeine can generate tolerance, or psychological dependence, and can become habit-forming. Sudden abstinence from caffeine ingestion can produce a series of symptoms such as headache, irritation, nervousness, anxiety, tremors, or dizzine

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