A team at Johns Hopkins University in Baltimore, Maryland, found that caffeine enhances certain memories for at least a day after they were formed.
Evidence for caffeine as a memory booster has been anecdotal until now.
This is because the process of registering memories -- say, reading a book ahead of an exam -- may happen in conditions where the person is eager to absorb and retain information.
This makes it hard to distinguish between someone's natural alertness and that derived from caffeine.
To strip out this confounding factor, a team led by Michael Yassa, an assistant professor of psychological and brain science, tried a different tack.
They asked 73 volunteers to look at images of a number of objects -- for instance, a plant, a basket, a saxophone, or a seahorse.
Afterwards, half of the group were given a 200 milligramme dose of caffeine -- roughly equivalent to two cups of strong espresso -- and the others a dummy pill known as a placebo.
Saliva samples were taken one, three and 24 hours later to measure caffeine levels.
The following day, both groups were asked to look at another set of pictures.
Some of the images were the same, others were new, and a few were similar -- for instance, a basket as before, but this time with one handle instead of two.
Both groups did well at distinguishing between old and new pictures, the researchers said.