File this under "stuff I should have realised by now": while it may appear innocuous, green tea is not a caffeine-free beverage.
Picture by gohomekiki
I quite often drink green tea in the office, and one of my lazy mental justifications has been "oh well, I'm not soaking up caffeine that way". But actually I am. As the ABC's Health & Wellbeing site explains:
Green tea and black tea contain the same amount of caffeine, as both come from the Camellia sinensis plant. Red tea or Rooibos tea comes from a different plant and contains no caffeine. According to the National Drug and Alcohol Research Centre at the University of New South Wales, the caffeine content of a typical 150 ml cup of tea varies from 30 to 100 mg, depending on how long the tea is infused and whether you brew with loose leaves or tea bags (strong loose-leaf tea yields the most caffeine).
In short: drinking green or black tea is a little better than coffee, but it's not an entirely caffeine-free experience. If you already knew this, well done you; why didn't you tell me earlier?
You can purchase caffeine-free green tea, and if you're dosing up in large amounts, that would be sensible. We've discussed what caffeine does to your brain before, so moderation is definitely advisable.
Caffeine [ABC Health & Wellbeing]