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.
Creatine is a substance that’s produced in the human body. It is initially produced in the kidneys, and the process is completed in the liver. It is then stored in the brain tissues and muscles, to support the energy demands of a human body. Athletes and bodybuilders take creatine supplements for relieving fatigue and increasing the recovery of the muscle tissues that are affected by vigorous physical activities. Apart from helping the tissues to recover faster, creatine also helps in enhancing the mental functions in sleep-deprived adults and it also improves the performance of difficult cognitive tasks.
These days, young, ambitious professionals prefer prescription stimulants—including methylphenidate (usually sold as Ritalin) and Adderall—that are designed to treat people with attention deficit hyperactivity disorder (ADHD) and are more common and more acceptable than cocaine or nicotine (although there is a black market for these pills). ADHD makes people more likely to lose their focus on tasks and to feel restless and impulsive. Diagnoses of the disorder have been rising dramatically over the past few decades—and not just in kids: In 2012, about 16 million Adderall prescriptions were written for adults between the ages of 20 and 39, according to a report in the New York Times. Both methylphenidate and Adderall can improve sustained attention and concentration, says Barbara Sahakian, professor of clinical neuropsychology at the University of Cambridge and author of the 2013 book Bad Moves: How Decision Making Goes Wrong, and the Ethics of Smart Drugs. But the drugs do have side effects, including insomnia, lack of appetite, mood swings, and—in extreme cases—hallucinations, especially when taken in amounts the exceed standard doses. Take a look at these 10 foods that help you focus.

Pop this pill and improve your memory. Swallow that one and reduce your cognitive decline. We see ads for such products all the time and I suspect they will increase as the baby boomers reach senior citizenhood. The most popular brain boosting supplements are fish oil pills and they are also probably the best studied ones. The results are not encouraging. When all the studies are pooled, we are left with the possibility of a barely significant improvement in recalling lists of words soon after they have been learned, but the effect does not last. Extracts of the ginkgo biloba tree are also popular, and here the prospects are even dimmer. There is no impact on memory, despite claims of increased circulation in the brain. And ginkgo can interfere with the action of anticoagulants and has also been shown to be an animal carcinogen.

In fact, when combined into a variety of different supplement “stacks” and taken in the correct dosage, these compounds – usually referred to as either smart drugs or nootropics (but now also including the category of psychedelics) – can completely change how your brain performs, including impacting receptor sites for neurotransmitters, altering levels of enzymes that break down specific neurotransmitters, changing cell membrane structures and thus controlling the movement of molecules inside and outside of the cell, increasing cerebral perfusion, which improves blood flow to the brain, affecting what are called “biogenic processes”, including neuronal cell creation or “neurogenesis”, and neuroendocrine regulation, regulating hormonal processes of the body specifically related to cognition (See additional studies here, here, here and here.).
One curious thing that leaps out looking at the graphs is that the estimated underlying standard deviations differ: the nicotine days have a strikingly large standard deviation, indicating greater variability in scores - both higher and lower, since the means weren’t very different. The difference in standard deviations is just 6.6% below 0, so the difference almost reaches our usual frequentist levels of confidence too, which we can verify by testing:

In 2011, as part of the Silk Road research, I ordered 10x100mg Modalert (5btc) from a seller. I also asked him about his sourcing, since if it was bad, it’d be valuable to me to know whether it was sourced from one of the vendors listed in my table. He replied, more or less, I get them from a large Far Eastern pharmaceuticals wholesaler. I think they’re probably the supplier for a number of the online pharmacies. 100mg seems likely to be too low, so I treated this shipment as 5 doses:

From the standpoint of absorption, the drinking of tobacco juice and the interaction of the infusion or concoction with the small intestine is a highly effective method of gastrointestinal nicotine administration. The epithelial area of the intestines is incomparably larger than the mucosa of the upper tract including the stomach, and the small intestine represents the area with the greatest capacity for absorption (Levine 1983:81-83). As practiced by most of the sixty-four tribes documented here, intoxicated states are achieved by drinking tobacco juice through the mouth and/or nose…The large intestine, although functionally little equipped for absorption, nevertheless absorbs nicotine that may have passed through the small intestine.
But it's not the mind-expanding 1960s any more. Every era, it seems, has its own defining drug. Neuroenhancers are perfectly suited to the anxiety of white-collar competition in a floundering economy. And they have a synergistic relationship with our multiplying digital technologies: the more gadgets we own, the more distracted we become and the more we need help in order to focus. The experience that neuroenhancement offers is not, for the most part, about opening the doors of perception, or about breaking the bonds of the self, or about experiencing a surge of genius. It's about squeezing out an extra few hours to finish those sales figures when you'd really rather collapse into bed; getting a B instead of a B-minus on the final exam in a lecture class where you spent half your time texting; cramming for the GREs (postgraduate entrance exams) at night, because the information-industry job you got after college turned out to be deadening. Neuroenhancers don't offer freedom. Rather, they facilitate a pinched, unromantic, grindingly efficient form of productivity.
It’s also loaded with vitamin C — in fact, just one cup provides you with 150 percent of your recommended daily intake. Its high-fiber levels mean that you’ll feel full quickly, too. If you’ve only chowed down on overcooked, tasteless broccoli, you’ll love my Crockpot Beef and Broccoli, Creamy Broccoli Soup and Broccoli Pesto Dip — they’ll turn you into a broccoli lover fast!
The use of cognition-enhancing drugs by healthy individuals in the absence of a medical indication spans numerous controversial issues, including the ethics and fairness of their use, concerns over adverse effects, and the diversion of prescription drugs for nonmedical uses, among others.[1][2] Nonetheless, the international sales of cognition-enhancing supplements exceeded US$1 billion in 2015 when global demand for these compounds grew.[3]