As for newer nootropic drugs, there are unknown risks. “Piracetam has been studied for decades,” says cognitive neuroscientist Andrew Hill, the founder of a neurofeedback company in Los Angeles called Peak Brain Institute. But “some of [the newer] compounds are things that some random editor found in a scientific article, copied the formula down and sent it to China and had a bulk powder developed three months later that they’re selling. Please don’t take it, people!”
A fancier method of imputation would be multiple imputation using, for example, the R library mice (Multivariate Imputation by Chained Equations) (guide), which will try to impute all missing values in a way which mimicks the internal structure of the data and provide several possible datasets to give us an idea of what the underlying data might have looked like, so we can see how our estimates improve with no missingness & how much of the estimate is now due to the imputation:
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More photos from this reportage are featured in Quartz’s new book The Objects that Power the Global Economy. You may not have seen these objects before, but they’ve already changed the way you live. Each chapter examines an object that is driving radical change in the global economy. This is from the chapter on the drug modafinil, which explores modifying the mind for a more productive life. 
Can brain enhancing pills actually improve memory? This is a common question and the answer varies, depending on the product you are considering. The top 25 brain enhancement supplements appear to produce results for many users. Research and scientific studies have demonstrated the brain boosting effects of nootropic ingredients in the best quality supplements. At Smart Pill Guide, you can read nootropics reviews and discover how to improve memory for better performance in school or at work.
Phillips told me that, much as he believes in neuroenhancers, he did not want to be "the poster boy for smart-in-a-pill". At one point, he said: "We really don't know the possible implications for long-term use of these things." (He recently stopped taking Provigil every day, replacing it with another prescription stimulant.) Nor does he think we need to be turning up the crank another notch on how hard we work. "But," he said, "the baseline competitive level is going to reorientate around what these drugs make possible, and you can choose to compete or not."
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This looks interesting: the Noopept effect is positive for all the dose levels, but it looks like a U-curve - low at 10mg, high at 15mg, lower at 20mg, and even lower at 30mg 48mg and 60mg aren’t estimated because they are hit by the missingness problem: the magnesium citrate variable is unavailable for the days the higher doses were taken on, and so their days are omitted and those levels of the factor are not estimated. One way to fix this is to drop magnesium from the model entirely, at the cost of fitting the data much more poorly and losing a lot of R2:

Recently I spoke on the phone with Barbara Sahakian, a clinical neuropsychologist at Cambridge University and the co-author of a 2007 article in Nature entitled "Professor's Little Helper". Sahakian, who also consults for several pharmaceutical companies, and her co-author, Sharon Morein-Zamir, reported that a number of their colleagues were using prescription drugs like Adderall and Provigil. Because the drugs are easy to buy online, they wrote, it would be difficult to stop their spread: "The drive for self-enhancement of cognition is likely to be as strong if not stronger than in the realms of 'enhancement' of beauty and sexual function." (In places like Cambridge, at least.)
Working memory has been likened to a mental scratch pad: you use it to keep relevant data in mind while you're completing a task. (Imagine a cross-examination, in which a lawyer has to keep track of the answers a witness has given and formulate new questions based on them.) In one common test subjects are shown a series of items - usually letters or numbers - and then presented with challenges: was this number or letter in the series? Was this one? In the working-memory tests, subjects performed better on neuroenhancers, though several of the studies suggested that the effect depended on how good a subject's working memory was to begin with: the better it was, the less benefit the drugs provided.
Feeling behind, I resolved to take some armodafinil the next morning, which I did - but in my hurry I failed to recall that 200mg armodafinil was probably too much to take during the day, with its long half life. As a result, I felt irritated and not that great during the day (possibly aggravated by some caffeine - I wish some studies would be done on the possible interaction of modafinil and caffeine so I knew if I was imagining it or not). Certainly not what I had been hoping for. I went to bed after midnight (half an hour later than usual), and suffered severe insomnia. The time wasn’t entirely wasted as I wrote a short story and figured out how to make nicotine gum placebos during the hours in the dark, but I could have done without the experience. All metrics omitted because it was a day usage.
Speaking of addictive substances, some people might have considered cocaine a nootropic (think: the finance industry in Wall Street in the 1980s). The incredible damage this drug can do is clear, but the plant from which it comes has been used to make people feel more energetic and less hungry, and to counteract altitude sickness in Andean South American cultures for 5,000 years, according to an opinion piece that Bolivia’s president, Evo Morales Ayma, wrote for the New York Times.

Alex remains enthusiastic about Adderall, but he also has a slightly jaundiced critique of it. "It only works as a cognitive enhancer insofar as you are dedicated to accomplishing the task at hand," he said. "The number of times I've taken Adderall late at night and decided that, rather than starting my paper, hey, I'll organise my entire music library! I've seen people obsessively cleaning their rooms on it." Alex thought that generally the drug helped him to bear down on his work, but it also tended to produce writing with a characteristic flaw. "Often I've looked back at papers I've written on Adderall, and they're verbose. They're labouring a point, trying to create this airtight argument. I'd produce two pages on something that could be said in a couple of sentences." Nevertheless, his Adderall-assisted papers usually earned him at least a B. They got the job done. As Alex put it: "Productivity is a good thing."
Because modafinil works in a manner similar to methylphenidate, it also bears similar risks. The improper dosage or abuse of modafinil may lead to the disrupted development of executive controls like decision-making and working memory. Modafinil’s effects may also depend upon the IQ of the taker. Two university studies determined that in a test of sustained attention, modafinil only improved cognition in the group with “lower” IQs. Although safer than other stimulants due to its milder effect on neurotransmitter levels, there are still risks associated with any kind of drug that affects dopaminergic neurotransmission, mostly because this can lead to addiction and, similar to a pornography user who needs increasingly fringe porn to achieve the same effect, can produce a resistance or lowered sensitivity to dopamine.
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According to the US Food and Drug Administration, "Piracetam is not a vitamin, mineral, amino acid, herb or other botanical, or dietary substance for use by man to supplement the diet by increasing the total dietary intake. Further, piracetam is not a concentrate, metabolite, constituent, extract or combination of any such dietary ingredient. [...] Accordingly, these products are drugs, under section 201(g)(1)(C) of the Act, 21 U.S.C. § 321(g)(1)(C), because they are not foods and they are intended to affect the structure or any function of the body. Moreover, these products are new drugs as defined by section 201(p) of the Act, 21 U.S.C. § 321(p), because they are not generally recognized as safe and effective for use under the conditions prescribed, recommended, or suggested in their labeling."[33]