depends... They give kids a doseage of either 10mg split AM and PM or 10mg AM and 10mg PM. 10mg for me is enough to get me going on a paper for hours. Usually takes about 15-20 minutes for effects to take place. If your worried about the side effects, they are minimal. The crash from it however is something i like to avoid. Also, it may raise blood pressure a bit so if your friend already has high blood pressure to begin with, the doseage should be watched.