A 75-mg serving of caffeine can increase attention and alertness, and a 160 to 600-mg dose may improve mental alertness, speed reasoning, and memory. However, caffeine is not a substitute for sleep.
If you do eat or drink too much caffeine, it can cause health problems, such as:
Restlessness and shakiness.
Insomnia.
Headaches.
Dizziness.
Fast heart rate.
Dehydration.
Anxiety.
Dependency, so you need to take more of it to get the same results.