Drinking large amounts of coffee or other caffeinated drinks could lead to hallucinations or seeing “ghosts”, a study suggests.

People who drink more than the equivalent of seven cups of instant coffee a day are more likely to see things or hear voices, and even report sensing the spirits of the dead, researchers say.

In a study of 200 students, those who consumed high amounts of caffeine were three times more likely to have heard a non-existent person’s voice than those who consumed less than one cup of instant coffee or its equivalent a day.

Besides coffee, the researchers considered sources such as tea, chocolate, “pep” pills and energy drinks. The students’ susceptibility to hallucinatory experiences and stress levels were also assessed.

Among the experiences reported were seeing things that were not there, hearing voices, and sensing the presence of dead people. The researchers from the University of Durham pointed out that hallucinations were not necessarily a sign of mental illness and that about 3 per cent of people regularly hear voices, but they believe that caffeine’s ability to exacerbate the effects of stress may explain the findings.

When under stress, the body releases a hormone called cortisol, which is produced in greater quantities after consuming caffeine. The extra cortisol boost could lead to hallucinations, the researchers suggest.

Simon Jones, a PhD psychology student who led the study, said: “This is a first step towards looking at the wider factors associated with hallucinations. Previous research has highlighted a number of important factors, such as childhood trauma, which may lead to clinically relevant hallucinations. Many such factors are thought to be linked to hallucinations, in part because of their impact on the body’s reaction to stress.

“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.”

High caffeine consumption is also associated with symptoms including nervousness, irritability, anxiety, muscle twitching, insomnia, headaches, and heart palpitations. But people who drink 250mg or less a day rarely experience any harmful symptoms, the researchers note.

The Department of Health advises people not to drink more than five single espressos a day - roughly seven instant coffees.

The highest natural caffeine content is found in filter coffee, a mug of which contains about 120mg of caffeine. Instant coffee contains roughly 75mg and espresso 107mg.

Dr Charles Fernyhough, co-author of the study, said that it only showed an association between caffeine intake and hallucination proneness, not a causal link.

“One interpretation may be that those students who were more prone to hallucinations used caffeine to help cope with their experiences,” he 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.”

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