So long as you are strategic about it, caffeine can actually help you when it comes to memory retention. In small doses, caffeine improves your alertness, productivity, mood, and ultimately your memory retention. However, too much, and you will be bouncing off the walls, negatively affecting your study session. So, caffeine = good, but drink it in the form of a nice coffee or tea, and not a massive energy drink. Keep it in small doses, and you should be good to go.