In some situations, the brain is performance-limited by the available fuel. Increase the fuel and you can temporarily get a performance boost.
The smart drug page definitely needs work. This page should be merged with it though. If you are writing about fuel alone, the only thing you can say is: drink glucose. Of course, amino acids and necessary constituents of neurotransmitters could be called "fuel," but they are not, simply because they provide signaling and building blocks, not energy.
Free-form discussion of this hack goes here.
Errata goes here.