Recent research has revealed that excessive intake of coffee can increase tendency to hallucinate. The researchers from the University of Durham found that people who drink more than seven cups of instant coffee a day were three times more likely to hallucinate than those who took just one.

Findings were based on the data collected from 200 students. The study subjects were asked about their intake of caffeine-containing products, hallucinatory experiences and stress levels.

Researchers said that caffeine's ability to exacerbate the effects of stress may explain the findings. When body is under stress it releases a hormone called cortisol, which is produced in greater quantities after consuming caffeine. The extra cortisol increases tendency to hallucinate.

Researchers pointed out that hallucinations are not necessarily a sign of mental illness and around 3% of people regularly hear voices.

Lead researcher, Psychologist Simon Jones, the PhD student said: "Previous research has highlighted a number of important factors, such as childhood trauma, which may lead to clinically relevant hallucinations."