Caffeine tolerance develops very quickly, especially among heavy coffee and energy drink consumers. Complete tolerance to sleep disruption effects of caffeine develops after consuming 400 mg of caffeine 3 times a day for 7 days. Complete tolerance to subjective effects of caffeine was observed to develop after consuming 300 mg 3 times per day for 18 days, and possibly even earlier.[57] Partial tolerance to caffeine has been observed in other areas. Studies with mice indicate that after a long period of caffeine exposure, the learning benefits of caffeine observed earlier cannot be found to any significant level. Considering that 80% to 90% of American adults consume caffeine daily, and their mean daily caffeine intake exceeds 200 mg/day,[58] it can be surmised that a large fraction of the U.S. adult population is completely tolerant to most of the effects of caffeine.
Seven days? Wow.
Weird, as my caffeine tolerance seems to have plummeted with age. A cup of coffee now makes me sweat, feel anxious and weakens my bladder. :)
Yeh, I had to move on to cocaine ‘n’ drain cleaner.