One of our readers wrote in with this question: I recently read about how drinking as many as seven cups of coffee per day can make me hallucinate. Is this true? I'm a pretty heavy coffee drinker, so I'd like to know.

Here's the answer:

For those that don't know, here's some background. Researchers at the University of Durham, in England surveyed two-hundred students about their daily consumption of coffee, energy drinks, and other caffeine products. They asked, among other things, if the students ever experienced hallucinations.

The results appeared to show that students who consumed the equivalent of seven cups of instant coffee were three times more likely to have heard a disembodied voice than students who consumed less caffeine. Heavy caffeine users were also more likely to sense the presence of dead people and see things that weren't there.

As for why caffeine may induce hallucinations, the researchers could only speculate. But they think it might have to do with cortisol–a hormone released during stress. Caffeine is known to make the body produce even more cortisol during stress.

None of this is solid proof that caffeine triggers hallucinations. First, it's possible that people already prone to hallucinations turn to caffeine as a way to self-medicate. Also, the study depended on the subject's self-reporting.

The only way to really find out if caffeine has anything to do with hallucination is to do a random controlled study, where several groups of subjects consume varying amounts of caffeine and are monitored in a controlled setting. Still, the study is an interesting first step toward learning more about how what we put in our bodies affects the ways we think and behave.