DEPRIVE coffee addicts of their morning fix and you will soon hear about it. But give them too much caffeine, and it turns out they will be the ones to start hearing things.

In the latest addition to the pile of research papers published on the bitter brown elixir, scientists have found that drinking five or more coffees a day is enough to increase a person's tendency to hallucinate. Caffeine lovers with high-stress lifestyles are most at risk.

Good shots .... Tom Thorburn, left, Luke Kneller and Toby Miles enjoy a cup of coffee or five at Toby’s Estate in Chippendale. Credit:Edwina Pickles

The study, published in the journal Personality and Individual Differences , measured the effect of stress and caffeine on 92 people. The participants were grouped according to self-reported stress levels and caffeine consumption. Those drinking five or more standard caffeinated drinks a day were classed as high caffeine users.

Participants were then asked to listen to white noise and to report when they also heard part of Bing Crosby's White Christmas coming through the white noise. The song was never played, and researchers measured the number of false alarms reported.