Most people who are trying to improve their cognitive abilities do so by trading off high quality work at one point of the day for some low quality brain power later on. This trade off means that people can work really hard and creatively at a certain point, but afterwards it will start to fall apart. There are ways to avoid this if you have the right mentality about your nootropics. For one thing, it is a good idea to take a scientific approach so that you do not have any problems with caffeine.
Avoiding caffeine crashes can be done in a few different ways. Some people handle the problem by just taking more caffeine, which is not a good idea because it builds tolerance and it hurts the adrenal system by constantly pumping more adrenaline into the system. Most of the time, people who get addicted to caffeine are doing so because they are just trying to keep chasing the high quality brain power that they have.
One alternative is to get an amino acid called L-theanine from green tea (which can be purchased here) that can help to balance out the caffeine. It is a naturally occurring amino acid that is healthy and promotes alpha brain waves. It also helps to prevent you from getting any of the troubles that many people have with caffeine crashes later on in the day.
Another alternative is to use a stimulant called theobromine along with the caffeine. Instead of taking a full dose of caffeine you can substitute some theobromine, which is a different molecule, but quite similar and has stimulating effects. If you are trying to improve your abilities from a cognitive perspective, this is one of the best places that you can start.