TL/DR: Take L-Theanine with caffeine to boost the positive effects of caffeine and reduce the negative effects. This is considered a Nootropic. It will make you "smarter."
Nootropics are basically vitamins that can pass through the blood-brain barrier and influence brain chemistry. The blood-brain barrier is as it sounds, a barrier between your circulatory system and your brain. A primary test a substance has to pass to be considered a nootropic is low toxicity. Tylenol alcohol, tabacco, and sugar are all going to be worse for your health than most substances labeled nootropics.
I assume your a responsible adult, so do your own research before consuming any of these substances. A great online community of Nootropic users, as well as a in depth FAQ can be found at reddit.com/r/Nootropics
The most simple and best price/performance ratio is a L-theanine + Caffine combonation. I personally like getting my caffeine from BulletProof coffee (a post on that in the future) but caffeine pills work just as well and are easier for measuring doses. The recommended does is twice as much L-theanine as caffeine. Example: 50 mg caffeine, 100 mg L-theanine. Its cheap and both can be found on Amazon.
On another note, all Nootropics are a little confused. The scientific community isn't sure what it means to be smart, or how intelligence works at a macro level in a chemistry sense. So these substances and their users are sincere, but keep in mind, most of the ones claiming to know, don't really know. Be careful, stay humble, and keep learning.