Studies have found that the effect of rumination on cortisol levels varies between groups, which may be because caffeine use and depression risk factors interact differently depending on the environment or other unknown factors.

People who regularly drink caffeine and tend to ruminate excessively do not show the typical decrease in cortisol levels that is linked to depression risk, indicating that caffeine might affect how the body responds to stress in this group.

People who regularly consume caffeine show a stronger cortisol response to stress, and this pattern was observed in two separate groups of young adults.

People who regularly consume caffeine show a stronger cortisol response when exposed to social stress, compared to those who do not.

Consuming caffeine on the same day as a stress test does not change the level of cortisol released in response to stress in healthy young adults. The pattern of cortisol response is more likely related to regular, long-term caffeine consumption than to a single dose.

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.