What they found was that participants had a noticeable mood boost following coffee, but this effect was strongest within 150 minutes of waking up. After that, the positivity faded, only picking up slightly again in the evening. Not surprisingly, this link between caffeine and good mood was greater when people were tired, but less pronounced when they were drinking coffee in social situations.

"Caffeine works by blocking adenosine receptors, which can increase dopamine activity in key brain regions – an effect that studies have linked to improved mood and greater alertness," said Professor Anu Realo from the University of Warwick.