1. Stomach upset and constipation
In Japan and China, it is common knowledge that you shouldn’t drink green tea on an empty stomach. The green tea tannins increase stomach acid. So, if you drink green tea before eating, it may give you a stomachache, a nauseous feeling, or cause constipation.
It is best to drink green tea after a meal or in-between meals. People with peptic ulcers or acid reflux should be especially careful. You can try adding milk if it continuously causes stomachaches.