Trippy. Heavy coffee drinkers tend to hallucinate, but the cause is unclear.

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Caffeine Linked to Hallucinations

If your cup of joe starts talking to you, chances are you're a caffeine addict. People who drink a lot of coffee or other caffeinated beverages are more likely to report hearing voices or having out-of-body experiences than those who go easy on the strong stuff, according to a new study.

The link between caffeine and hallucinations makes sense physiologically. When stressed, the body amps up its production of the hormone cortisol, which can cause people to see and hear things that aren't there. Cortisol is also regulated by caffeine, which increases hard-core coffee and tea drinkers' responses to stress.

Intrigued by the connection, psychologists Simon Jones and Charles Fernyhough of Durham University in the U.K. designed an online survey that was e-mailed to university students. The 200-plus participants, most of them women, answered questions such as "How often do you drink ... brewed coffee?" and ranked the relevance of statements such as "I have had a sensation ... that I left my body temporarily."

On average, the students drank the caffeine equivalent of about three cups of strong tea or instant coffee per day, Jones and Fernyhough report today in the journal Personality and Individual Differences. More importantly, the data show that individuals who consumed more caffeine were more likely to hallucinate.

Although the results are intriguing, Jones says that the study does not prove that caffeine causes hallucinations. People who tend to see or hear things may just be more naturally prone to drink a lot of coffee, he says. "And we can't rule out the fact that participant's experiences might be related to alcohol or illegal drugs."

Psychologist John Stirling of the Manchester Metropolitan University in the U.K. says research going back to the 1980s suggests a link between caffeine and hallucinations. But Stirling is skeptical of a causal relationship, pointing out that if people can develop a tolerance to caffeine they may also develop a tolerance to hallucinations.

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