Although green tea is completely safe, there can be negative side effects from gross overconsumption. In most cases these side effects are very minor. Let’s take a look...

Caffeine Side Effects

Nearly all of the negative side effects of green tea are related its caffeine content. Even though caffeine is also responsible for a few of the positive benefits, in some cases overconsumption can lead to:

• Upset stomach
• Restlessness
• Irritability
• Sleeping problems
• Dizziness

Pregnancy and Caffeine

Some health organizations advise pregnant women to limit their caffeine consumption to 300 mg per day, as caffeine has been associated with an increased risk of miscarriage and low birth weights.

Oxalates & Kidney Damage

Tea contains an organic acid called oxalate which can cause kidney damage if overconsumed. Once again, this side effect is very unlikely to happen as it requires massive amounts of tea to cause any damage.

Allergies

People with known allergy/hypersensitivity to caffeine or tannin should avoid green tea as skin rashes and hives have been reported with caffeine ingestion.

Medications & Green Tea

If you are being treated with any of the following medications, you should speak with your physician before drinking large amounts of green tea or taking green tea extract.

Aspirin
Aspirin prevents blood platelets from clotting, and to an extent so does green tea. Using them both together may increase your risk of bleeding without clotting.

Adenosine
Adenosine is a medication used for stabilizing an irregular heart rhythm. Green tea may inhibit it from working properly. This medication is usually only used in a hospital.

Clozapine
The anti-psychotic effects of the medication clozapine may be reduced if taken less than 40 minutes after drinking green tea.

Monoamine oxidase inhibitors (MAOIs)
When taken together with MAOIs (used to treat depression), green tea can cause a severe increase in blood pressure.

Lithium
Lithium is another medication used to treat depression. Green tea has been shown to reduce the levels of lithium in the blood, so it may interfere with the medication.

Blood thinners
Green tea contains vitamin K, which can make the blood thinner warfarin ineffective.

Final Word on Green Tea Side Effects

Don’t be alarmed in the slightest by these side effects. The fact is, Oolong tea does vastly more good than harm, and, unless you drink enough to almost drown yourself, you won’t see any negative effects at all.