Sensitivity varies wildly for for different people. I seem to have a very low sensitivity - the only time I have felt the effects was on a barista course where I think I was up to 6-7 double espresso shots in the 90 minutes.
I drink espresso in the morning, black coffee through out the day and stop before dinner. It's around 4-8 mugs every day. On holidays I often go a days without any coffee for various reasons with no ill effects. I have gone an entire month substituting coffee with water to test the hypothesis that it doesn't really affect me and I felt no different. HR, BP, sleep quality, tiredness, mental performance, digestion all remained stable.
My neighbour gets a headache if he skips coffee for a day.
I drink espresso in the morning, black coffee through out the day and stop before dinner. It's around 4-8 mugs every day. On holidays I often go a days without any coffee for various reasons with no ill effects. I have gone an entire month substituting coffee with water to test the hypothesis that it doesn't really affect me and I felt no different. HR, BP, sleep quality, tiredness, mental performance, digestion all remained stable.
My neighbour gets a headache if he skips coffee for a day.