The effect of coffee is illustrated with the table below. A 20-point reduction in drowsiness is guaranteed to remove the Sleepy status and to reduce the first Need Sleep status. It will also remove the initial stages of the second Need Sleep status. It is possible to go into negative drowsiness, with the only known effect taking a bit longer to get the Sleepy status again, also, you can mix milk with coffee to get milk coffee, it has the benefits of both but with slightly less effect.
Neither cursed nor blessed coffee has any additional effect.