In fact, compared to the coffee drinkers allowed to have a cup, those suffering cravings had close to a 50 per cent lower proportion of correct responses. However, those who scored badly thought they had done just as well as usual.
Previous research has shown that heavy coffee drinkers pay exaggerated attention to the drink in a similar way drug users do to heroin and cocaine.
The study, published in the journal Memory, states that coffee-drinking, when it becomes a habit, requires cognitive processing in the brain to stop people picking up a cup of coffee.
It is this extra activity which leaves less space for other tasks, meaning it is harder to remember things.