I agree. I'm deep into specialty coffee and I love making and drinking coffee a lot, but three cups is already higher than what I drink on a normal day. Also, most of the time when I go above this threshold, I drink decaf.
I drink a small cup in the morning (like 250 ml) and 1-2 Moka pot espressos (like one shot). This typically happens between 7-10am. No more coffee after that most of the time. I like to keep it in the morning routine with breakfast. Green tea and water in my afternoons.
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.
It depends on how much caffeine is in your cup. Rather than measuring the size of a cup, I would go by the amount of coffee, as in the weight of the beans, used to brew it. The actual amount of caffeine is not as easy to measure, and even for the same kind of beans, there is natural variation.
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.
caffeine extraction is largely a function of time in contact with water. Espresso is quite quick brew, so has less caffeine than other brewing methods (yes, there are plenty of other factors)
There is no realistic scenario where, no matter your extractions or bean selections, 6-10 shots of espresso a day is not an enormous amount of caffeine
A grande americano at Starbucks is a 16 oz drink with three shots of espresso. Have one in the morning and one in the afternoon and you are at six shots of espresso. That doesn't seem all that enormous to me.
The reactions to your comment got me curious enough to check. The mug I use for coffee and tea holds almost exactly 400 mL when comfortably full and I used to drink 2 of those per day (across 12 hours or so). Based on that, personally I'd consider ~800 mL of black coffee to be on the high end of moderate consumption.
3-5 is moderate? To me, 3 is already high.
Also, sample size is pretty low and they're all Irish.