Researchers in the UK found that people who ingest a lot of caffeine, for instance by drinking lots of coffee, tea, and caffeinated energy drinks, are more likely to report experiencing hallucinations, including hearing voices and seeing things and people that are not there.
The research, which was funded by the UK's Economic and Social Research Council and the Medical Research Council, was done by scientists at Durham University, and is published as an academic paper in the journal Personality and Individual Differences.
Defined as consuming more than the equivalent of seven cups of coffee a day, a high caffeine user was three times more likely to have heard a person speak when there was nobody there, compared to low caffeine users (those who had less than the equivalent of one cup of coffee a day), said lead author Simon Jones, a PhD student, and Dr Charles Fernyhough, both from Durham University's Psychology Department.
Jones and Fernyhough said they hoped their discovery will open the door to a new understanding of how different types of food can affect people's propensity to have hallucinations and thereby help people cope with them.
For the study they asked 200 students about their caffeine intake, including sources like coffee, tea, energy drinks, chocolate, and caffeine tablets, and assessed their proneness to hallucinations. Some of the experiences reported including seeing people who weren't there, hearing voices, and sensing the presence of people who were dead.
One possible explanation, said the authors, was that caffeine amplifies the effects of stress, by boosting the release of the stress hormone cortisol.
Explaining why they did the research, Jones said previous studies have linked hallucination to the stress response, and: "Given the link between food and mood, and particularly between caffeine and the body's response to stress, it seems sensible to examine what a nutritional perspective may add."