First was a combination of L-theanine and aniracetam, a synthetic compound prescribed in Europe to treat degenerative neurological diseases. I tested it by downing the recommended dosages and then tinkering with a story I had finished a few days earlier, back when caffeine was my only performance-enhancing drug. I zoomed through the document with renewed vigor, striking some sentences wholesale and rearranging others to make them tighter and punchier.
The greatly increased variance, but only somewhat increased mean, is consistent with nicotine operating on me with an inverted U-curve for dosage/performance (or the Yerkes-Dodson law): on good days, 1mg nicotine is too much and degrades performance (perhaps I am overstimulated and find it hard to focus on something as boring as n-back) while on bad days, nicotine is just right and improves n-back performance.
Lebowitz says that if you're purchasing supplements to improve your brain power, you're probably wasting your money. "There is nothing you can buy at your local health food store that will improve your thinking skills," Lebowitz says. So that turmeric latte you've been drinking everyday has no additional brain benefits compared to a regular cup of java.
One reason I like modafinil is that it enhances dopamine release, but it binds to your dopamine receptors differently than addictive substances like cocaine and amphetamines do, which may be part of the reason modafinil shares many of the benefits of other stimulants but doesn’t cause addiction or withdrawal symptoms.   It does increase focus, problem-solving abilities, and wakefulness, but it is not in the same class of drugs as Adderall, and it is not a classical stimulant. Modafinil is off of patent, so you can get it generically, or order it from India. It’s a prescription drug, so you need to talk to a physician.
Methylphenidate – a benzylpiperidine that had cognitive effects (e.g., working memory, episodic memory, and inhibitory control, aspects of attention, and planning latency) in healthy people. It also may improve task saliency and performance on tedious tasks. At above optimal doses, methylphenidate had off–target effects that decreased learning.