Drinking too much coffee can give people hallucinations and increase stress levels, according to new research.
The study by scientists at the University of Durham found that people who drink more than seven cups of instant coffee a day not only are more likely to hallucinate but may even think they can sense ghosts.
The researchers found that "high" caffeine users were three times more likely to have heard a voice that was not there than "low" users who consumed less than one cup of instant coffee.
They studied 200 students and asked them about their typical intake of caffeine, while assessing the students' susceptibility to hallucinations and stress.
Sensing the presence of the dead, seeing things that were not there and hearing voices were among the experiences reported by the students.
The stress hormone, cortisol, is produced in greater quantities after consuming caffeine and the scientists believe these findings suggest this extra boost of cortisol could create hallucinations.
Dr Charles Fernyhough, from the university's psychology department, said: "More work is needed to establish whether caffeine consumption, and nutrition in general, has an impact on those kinds of hallucination that cause distress."