Green tea (Camellia sinensis)

Green tea, as a popularly consumed beverage, is generally non-toxic7. No severe adverse effects have been reported in association with medicinal use of green tea8.
The above Cochrane review concluded that drinking green tea appears to be safe at moderate, regular and habitual use.5

Adverse events

In response to the publication of adverse event case reports involving green tea products, one systematic review by the US Pharmacopeia checked the safety of green tea extracts9. The review found a total of 216 case reports on green tea products including 34 reports concerning liver damage among which 27 pertaining to liver damage were categorized as possible causality and 7 as probable causality. Clinical pharmacokinetic and animal toxicological information indicated that consumption of green tea concentrated extracts on an empty stomach was more likely to lead to adverse effects than consumption in the fed state. Based on this safety review, it was determined that when dietary supplement products containing green tea extracts were used and formulated appropriately, the unawareness of significant safety issues would prohibit monograph development, provided a caution statement was included in the labeling section. Following this decision, monographs may be produced for green tea extracts, and verification may be offered for programmes related to that dietary ingredient.

Contraindications

Pregnant women, nursing mothers and patients with cardiac problems are usually advised to avoid or limit their intake to two cups daily10. In general, the stimulatory effect from green tea is considerably less than that of coffee7.

People with known allergy or hypersensitivity to caffeine or tannin should avoid green tea.8

Warnings

Consumption of high doses of green tea or green tea extract (equivalent to five liters per day) may cause nausea, vomiting, abdominal bloating and pain, dyspepsia, flatulence, and diarrhoea8. Excess consumption of caffeine from green tea may also cause central nervous system stimulation such as dizziness, insomnia, tremors, restlessness and confusion, and diuresis (increasing urine output), irregularities in heart rate, and psychomotor agitation8.