Glucose tablets are used by elite athletes, only under strict medical supervision, to replenish muscle glycogen reserves.
For example, the pill Messi ate would have given his muscles a quick burst energy, something that lead to the Argentinian superstar scoring his 100th European goal later on in the encounter at the Nou Camp.
There is, however, some debate as to when is the best time to take the tablet. Some experts say it will enhance performance after 15 minutes of exercise, while others claim it is best to take after warming up and before the main event.
According to 'Catalunya Radio', Barcelona's medical team decided their star man needed a dose for this particular match, meaning it is not something Messi does on a regular basis.