The evidence? Found helpful in reducing bodily twitching in myoclonus epilepsy, a rare disorder, but otherwise little studied. Mixed evidence from a study published in 1991 suggests it may improve memory in subjects with cognitive impairment. A meta-analysis published in 2010 that reviewed studies of piracetam and other racetam drugs found that piracetam was somewhat helpful in improving cognition in people who had suffered a stroke or brain injury; the drugs’ effectiveness in treating depression and reducing anxiety was more significant.
In paired-associates learning, subjects are presented with pairs of stimuli and must learn to recall the second item of the pair when presented with the first. For these tasks, as with tasks involving memory for individual items, there is a trend for stimulants to enhance performance with longer delays. For immediate measures of learning, no effects of d-AMP or MPH were observed by Brumaghim and Klorman (1998); Fleming et al. (1995); Hurst, Radlow, and Weidner (1968); or Strauss et al. (1984). However, when Hurst et al.’s subjects were tested a week later, they recalled more if their initial learning had been carried out with d-AMP than with placebo. Weitzner (1965) assessed paired-associates learning with an immediate cued-recall test and found facilitation when the associate word was semantically related to the cue, provided it was not also related to other cue words. Finally, Burns, House, French, and Miller (1967) found a borderline-significant impairment of performance with d-AMP on a nonverbal associative learning task.
Of all the smart drugs in the world, Modafinil is most often touted as the best. It’s a powerful cognitive enhancer, great for boosting alertness, and has very few, mild side effects that most healthy users will never experience. And no, you can’t have any. Sorry. Modafinil is a prescription medication used to treat disorders like narcolepsy, shift work sleep disorder, and for those who suffer from obstructive sleep apnea.
Texas-based entrepreneur and podcaster Mansal Denton takes phenylpiracetam, a close relative of piracetam originally developed by the Soviet Union as a medication for cosmonauts, to help them endure the stresses of life in space. “I have a much easier time articulating certain things when I take it, so I typically do a lot of recording [of podcasts] on those days,” he says.
Because smart drugs like modafinil, nicotine, and Adderall come with drawbacks, I developed my own line of nootropics, including Forbose and SmartMode, that’s safe, widely available, and doesn’t require a prescription. Forskolin, found in Forbose, has been a part of Indian Ayurvedic medicine for thousands of years. In addition to being fun to say, forskolin increases cyclic adenosine monophosphate (cAMP), a molecule essential to learning and memory formation. 
In addition, the cognitive enhancing effects of stimulant drugs often depend on baseline performance. So whilst stimulants enhance performance in people with low baseline cognitive abilities, they often impair performance in those who are already at optimum. Indeed, in a study by Randall et al., modafinil only enhanced cognitive performance in subjects with a lower (although still above-average) IQ.
(People aged <=18 shouldn’t be using any of this except harmless stuff - where one may have nutritional deficits - like fish oil & vitamin D; melatonin may be especially useful, thanks to the effects of screwed-up school schedules & electronics use on teenagers’ sleep. Changes in effects with age are real - amphetamines’ stimulant effects and modafinil’s histamine-like side-effects come to mind as examples.)
I am not alone in thinking of the potential benefits of smart drugs in the military. In their popular novel Ghost Fleet: A Novel of the Next World War, P.W. Singer and August Cole tell the story of a future war using drug-like nootropic implants and pills, such as Modafinil. DARPA is also experimenting with neurological technology and enhancements such as the smart drugs discussed here. As demonstrated in the following brain initiatives: Targeted Neuroplasticity Training (TNT), Augmented Cognition, and High-quality Interface Systems such as their Next-Generational Nonsurgical Neurotechnology (N3).
White, Becker-Blease, & Grace-Bishop (2006) 2002 Large university undergraduates and graduates (N = 1,025) 16.2% (lifetime) 68.9%: improve attention; 65.2:% partying; 54.3%: improve study habits; 20%: improve grades; 9.1%: reduce hyperactivity 15.5%: 2–3 times per week; 33.9%: 2–3 times per month; 50.6%: 2–3 times per year 58%: easy or somewhat easy to obtain; write-in comments indicated many obtaining stimulants from friends with prescriptions
Panax ginseng – A review by the Cochrane Collaboration concluded that "there is a lack of convincing evidence to show a cognitive enhancing effect of Panax ginseng in healthy participants and no high quality evidence about its efficacy in patients with dementia." According to the National Center for Complementary and Integrative Health, "[a]lthough Asian ginseng has been widely studied for a variety of uses, research results to date do not conclusively support health claims associated with the herb."