However, the group who had received caffeine were significantly better than the placebo group at identifying which images were “similar” rather than “old”, which Yassa says is a harder task.

He concludes that caffeine enhances long-term memory by improving the process of memory consolidation. “This doesn’t mean people should only drink coffee after they’ve studied, and not before,” says Yassa. “I think you would get the boost regardless.” That’s because the process of consolidation is likely to begin as soon as new memories form.

However, caffeine isn’t much use once consolidation is finished. The team ran a second experiment in which caffeine wasn’t administered until one hour before the memory test, to check for any effects on memory retrieval. They found no such effect. “So let’s say you studied without coffee and decided to drink a cup right before an exam – that’s not going to help you retrieve memories better,” says Yassa.