Even when people drink 300 mg of caffeine daily, their cortisol levels stay higher than normal for up to six hours after an afternoon dose, showing that the body's stress response system does not fully adjust to this level of caffeine intake.

Taking 600 mg of caffeine per day for five days leads to a smaller increase in cortisol levels after a later caffeine dose compared to taking 300 mg per day, suggesting the body's stress hormone system adjusts more strongly at higher doses.

Taking 300 or 600 milligrams of caffeine daily for five days lowers the cortisol spike that occurs when you later take another 250 milligrams of caffeine, but cortisol levels still rise significantly, especially after afternoon doses, showing that the body does not fully adjust to caffeine over this period.

Even after taking 600 mg of caffeine daily for five days, the body still shows a measurable increase in cortisol levels after a subsequent dose, indicating that the stress response to caffeine does not fully disappear with short-term daily use.

After five days without caffeine, the body's cortisol response to a 250 mg dose of caffeine returns to its original strength, suggesting that tolerance to caffeine is temporary and linked to recent use, not permanent changes in the body.

Consuming 750 mg of caffeine daily in three doses increases cortisol levels throughout the day when individuals are exposed to mental stress, physical exercise, or eating after exercise, and this increase occurs similarly in both men and women, though the overall stress response size may differ by sex.