I'd say 3 is still moderate and really common. 5 is getting on the high'ish side.
Several of us here drink more than that.
Perhaps they even use US coffee cup size, which is 118ml?
Honestly, using an unit of measurement that varies from 118ml to 250ml in a scientific paper brings the whole paper into question.
woa where is half a liter of coffee a "normal" portion?
A NORMAL mug of 500ml??? this is insanity to me
For a traditional Italian espresso, about 7g of coffee beans are extracted. For a third-wave double espresso, it's usually 18g or more.
In my opinion, 10x7g is a lot. 2x12g is more than enough for me.
That's a bit over the recommended limit of 400mg a day the Mayo Clinic, FDA, etc. recommend. Not sure it it qualifies as 'enormous' or not.
Personally, I don't feel any kind of "drug like" effects from this routine. I wonder about the strength of coffee people are drinking and the effects of drinking throughout the day rather than just the morning.
Anecdotally, during grad school I drank more per serving and throughout the day, and I certainly felt quite different than my current routine.
Like most things, I think people need to find some moderation/balance.