Performing further away from one’s preferred time of day increases false memories, and the effects of caffeine

False memories occur when an individual may remember an experience or event differently from the way it’s actually happened or misremember that it even happened at all. Previous research has shown that the presence of false memories may be affected by subtle external factors such as sleep duration, caffeine intake, or the time of day (ToD) of testing. However, the effects of a wide range of sleep, tiredness, ToD and caffeine variables, specifically at the time of testing or prior to testing has rarely been explored. Fifty-seven cognitively-healthy adults completed a sleep, tiredness and caffeine questionnaire which assessed a range of variables including questions about habitual and current sleep patterns, tiredness and caffeine factors, followed by a false memory task. Results showed that (i) as participants performed further away from their subjectively reported preferred ToD the number of false memories increased and (ii) caffeine intake prior to testing reduced the number of false memories made when people were performing further away from their preferred ToD. These findings highlight the need to consider one’s subjective ToD preference for taking part in false memory tasks, and prior caffeine intake on the development of false memories in clinical, research and legal settings.