As early as the Stone Age, humans had already begun to use caffeine. Early people discovered that chewing the seeds, bark, or leaves of certain plants had the effect of relieving fatigue and refreshing the mind. It wasn't until many years later that people discovered that steeping these plants in hot water could increase the effectiveness of caffeine. Many cultures have myths about ancient people discovering these plants. However, recent research shows that drinking too much caffeine can cause hallucinations.
A rigorous study by Durham University in the UK found that people who consumed the equivalent of more than seven cups of instant coffee a day were twice as likely to experience hallucinations as those who drank one cup a day. Perhaps people who have hallucinations are inherently more anxious, which in turn leads them to consume more caffeine.
In addition, researchers also found that the mechanism by which caffeine causes hallucinations may be cortisol. The human body produces more cortisol after ingesting caffeine, which may in turn lead to hallucinations. This study also further illustrates that the amount of caffeine people consume daily may directly affect their health.
This research will continue to investigate whether people experience hallucinations because of caffeine intake, or whether people consume more caffeine when they are under stress.