As usual: always consume in moderation to prevent getting green tea extract side effects.
Drinking freshly brewed green a lot, I never encountered any side effects. I do agree that one has to go a few times more to the toilet, which again is good exercise to help burning some extra fat 
.
Of course when you take green tea extract, the concentrated amount of the green tea in the extract can be overdosed much easier.
Main side effect however is caused by the caffeine. Caffeine can keep you awake at night. Green tea contains much less caffeine compared to normal tea and coffee. For me: brewing fresh green tea never developed into insomnia, even after drinking huge amounts of green tea.
If you notice getting sleeping problems after taking green tea extract, give the green tea extract to a friend who won’t suffer insomnia side effects. Then go and source for caffeine free green tea extract for yourself.
Other green tea side effects noted are:
- headache,
- heart palpitations (that sounds again like a symptom of caffeine overdose),
- restlessness,
- vomiting and nausea,
- diarrhea or the opposite: constipation.
If you love milk, the above side effects can be eliminated by adding some milk into your green tea. I do that from time to time before I go to sleep.
When it comes to green tea extract side effects, people with health problems like:
- heart problems,
- stomach ulcers,
- kidney disorders and
- psychological disorders,
… may experience green tea extract side effects easier.
Always ask your doctor’s opinion about how green tea extract could interfere with any other medications you take or health problems you have.
I am convinced that you can get more easily pesticide poisoning from eating large amounts of strawberries (like what my brother suffers from each time he eats strawberries) than suffering from green tea extract side effects!
