Unsuprisingly, it wasn't intended that this tea instantly restores 100% of your hitpoints when you drink it. It's only supposed to boost the max hitpoints if you are at full health.
We have now fixed this, so the effects of the tea are now as follows:
I'm posting this news to warn you this has changed. So please DONT go fighting huge great monsters with only tea to heal you, it won't be a good idea!