Washington: Drinking coffee in moderation may be okay, but downing too much -- say five or more cups of the beverage daily -- can cause hallucinations, says a study.
Researchers at La Trobe University have found that drinking five cups of coffees or more a day may be enough to increase one`s tendency to hallucinate because of caffeine in it, which is the most commonly used psychoactive drug.
Coffee and other caffeinated beverages such as tea, soft-drinks and energy drinks access the stimulant and when taken in large quantities increase tendencies to hallucinate according to lead researcher Professor Simon Crowe.
In their study, the researchers measured the effect of stress and caffeine with 92 non-clinical participants. Five coffees a day or more was found to be enough to increase the participant`s tendency to hallucinate, said Prof Crowe.
"High caffeine levels in association with high levels of stressful life events interacted to produce higher levels of `hallucination` in non-clinical participants, indication that further caution needs to be exercised with the use of this overtly `safe` drug," he said.
The participants were assigned to either a high or a low stress condition and a high or a low caffeine condition on the basis of self-report. They were then asked to listen to white noise and to report each time they heard Bing Crosby`s rendition of "White Christmas" during the white noise.
The song was never played. The results indicated that the interaction of stress and caffeine had a significant effect on the reported frequency of hearing "White Christmas".
The participants with high levels of stress or consumed high levels of caffeine were more likely to hear the song.
"There is a link between high levels of stress and psychosis, and caffeine was found to correlate with hallucination proneness. The combination of caffeine and stress affect the likelihood of an individual experiencing a psychosis-like symptom," said Prof Crowe.
According to the researchers, their study also helped to explain the mechanism by which stress may facilitate the symptoms of schizophrenia in non-clinical samples.
"The results also support both the diathesis- stress model and the continuum theory of schizophrenia in that stress plays a role in the symptoms of schizophrenia and that everyone, to some degree, can experience these symptoms.
"This was demonstrated by a significant effect of stress on the occurrence of hallucinatory experiences," added Prof Crowe.